Hooking up is not illegal in the United States when it happens in private between adults who both freely agree to it. The Supreme Court settled that in 2003 when it struck down a Texas sodomy law and held that adults have a constitutional right to private sexual conduct free of government interference.1Justia Law. Lawrence v. Texas, 539 U.S. 558 (2003) The law draws hard lines, though, around consent, age, where it happens, whether money changes hands, hidden health risks, and what gets recorded. Cross one of those lines and the same encounter becomes a crime.
Consent Is Where Legal Becomes Illegal
Every sexual encounter is lawful or criminal based on one question: did everyone freely agree? Legally, consent means a person voluntarily and willfully agrees to participate, has enough mental capacity to understand what they’re agreeing to, and acts without coercion, fraud, or duress.2Legal Information Institute. Consent Consent attaches to each specific activity, and it can be withdrawn at any point. Once someone says stop, continuing is a crime.
A person cannot give valid consent when incapacitated. That covers intoxication, unconsciousness, or a mental or developmental condition that prevents them from understanding the situation.2Legal Information Institute. Consent Someone who is blackout drunk or passed out cannot agree to sex. If the other person proceeds anyway, sexual assault charges follow regardless of what happened earlier in the night.
Drugging a partner carries some of the most severe penalties in criminal law. Under federal law, distributing a controlled substance to someone without their knowledge with intent to commit a violent crime, including rape, is punishable by up to 20 years in prison.3Office of the Law Revision Counsel. 21 USC 841 – Prohibited Acts A The statute specifically names GHB, ketamine, and flunitrazepam (Rohypnol), and using the internet to distribute any of them carries the same 20-year maximum. Aggravated sexual abuse committed by rendering someone unconscious or drugging them can draw a life sentence.4U.S. Department of Justice. Criminal Resource Manual 1982 – Aggravated Sexual Abuse
Age of Consent and Statutory Rape
Having sex with someone under the age of consent is a crime even if the younger person willingly participated. The age of consent ranges from 16 to 18 depending on the state.5U.S. Department of Health and Human Services. Statutory Rape – A Guide to State Laws and Reporting Requirements Statutory rape laws treat sexual activity below that age as inherently coercive, regardless of what either person believed in the moment.
Penalties are severe. Depending on the ages involved and the jurisdiction, charges range from misdemeanors to serious felonies carrying years or decades in prison. A conviction almost always triggers mandatory sex offender registration, which can last a lifetime.
Close-in-Age Exemptions
Roughly 30 states have “Romeo and Juliet” laws that soften the rule when both people are close in age. A 17-year-old dating a 15-year-old is treated differently from an adult targeting a child. The details vary. Some states allow a two-year gap, others up to five. Rather than legalizing the conduct outright, these provisions typically reduce felony charges to misdemeanors or provide a defense that avoids sex offender registration. If you’re a young adult in a relationship with someone near the age of consent, the specific rule in your state matters a great deal.
Did Not Know Their Age
Many states treat statutory rape as a strict liability crime, which means the defendant’s belief about age is irrelevant. Some states allow a reasonable mistake-of-age defense, particularly when the minor is close to the age of consent and the defendant had genuine reason to believe they were older. The burden falls on the adult, and plenty of jurisdictions reject the defense entirely. The safe assumption is that you are responsible for verifying age, because in most places you are.
Sex in Public
Constitutional protection for private conduct does not reach public spaces. Public indecency and indecent exposure laws prohibit sexual acts or nudity in places visible to others, including parks, streets, parking lots, and a car on a public road.
“Public” reaches further than most people expect. You do not have to be on a sidewalk. Courts have found that private property counts when the conduct is visible from a public area, like sex near an open window or on a balcony facing a street. The question is visibility, not who owns the property.
A first offense is typically a misdemeanor, with penalties running from fines to up to a year in county jail depending on the jurisdiction. The bigger risk is escalation. Repeat offenses become felonies in many states, and some jurisdictions require sex offender registration for any indecent exposure conviction. That registration requirement can last a decade or longer and shapes where you can live and work.
Paying for Sex
A hookup becomes illegal the moment money or anything of value is exchanged for sexual activity. Prostitution, meaning engaging in or agreeing to sexual conduct for a fee, is a crime throughout the United States, with the sole exception of licensed brothels in certain rural Nevada counties.6Legal Information Institute. Prostitution Solicitation, meaning offering or requesting sexual acts for compensation, is equally illegal.
A first offense is generally a misdemeanor. Fines typically run from a few hundred to a couple thousand dollars, and jail sentences of up to six months to a year are possible depending on the jurisdiction. Charges escalate quickly: repeat offenses, involvement of minors, or proximity to a school zone can push the case into felony territory. An arrest record for solicitation can show up on background checks and damage careers even when the charges are later dropped.
Having Sex With a Known STI
Knowingly having sex without disclosing a sexually transmitted infection can be a crime. Roughly three dozen states have laws specifically addressing criminal transmission of STIs, with most focused on HIV. To convict, prosecutors generally must prove the defendant knew they were infected and either intentionally exposed a partner or acted recklessly. Simply being unaware of an infection is not criminal.
In many of these states, disclosure provides a legal safe harbor: if you tell your partner and they consent anyway, no crime has been committed even if transmission occurs. Some states do not recognize that informed-consent exception, which means the act itself can be prosecuted regardless of what the partner knew. Penalties range from misdemeanors to serious felonies, especially for HIV-related offenses, where some states impose sentences comparable to assault.
Civil liability is a separate risk. A person who contracts an STI from a partner who knew and said nothing can sue for medical expenses, lost wages, and emotional distress, generally within two to six years from discovery of the infection depending on the state.
Recording and Sharing What Happened
Consent to sex is not consent to being filmed. Recording a sexual encounter without the other person’s knowledge or permission is a separate crime. Under federal law, intentionally capturing an image of someone’s private areas without consent, in circumstances where they have a reasonable expectation of privacy, is punishable by up to one year in prison and fines.7Office of the Law Revision Counsel. 18 USC 1801 – Video Voyeurism The federal statute applies on federal property, military bases, and similar jurisdictions, but nearly every state has its own voyeurism law reaching the same conduct more broadly. “Capture” covers video, photographs, and any other recording method.
Distributing intimate images of someone without their permission, often called “revenge porn,” is now illegal in all 50 states and Washington, D.C. These laws apply whether the images were originally taken consensually or not. What matters is whether the person depicted agreed to the images being shared.
At the federal level, the TAKE IT DOWN Act, signed into law in May 2025, makes it a federal crime to knowingly publish intimate images of a person without their consent, including AI-generated deepfakes. The law also requires social media platforms and websites to remove such content within 48 hours of being notified by a victim. Violations carry criminal penalties including prison time, fines, and mandatory restitution.8U.S. Congress. S.146 – TAKE IT DOWN Act, 119th Congress (2025-2026)
If One of You Is Married
About 16 states still have criminal adultery statutes on the books, so a hookup involving a married person technically violates the law in those places. Prosecutions are vanishingly rare. The real legal consequence of an extramarital encounter plays out in divorce court. In states that allow fault-based divorce, adultery can influence alimony and property division, with courts most interested in whether the cheating spouse spent significant marital funds on the affair. When a spouse depletes shared assets on an extramarital relationship, the other spouse can argue for a larger share of what remains.
The Consequence Most People Miss: Sex Offender Registration
Under the federal Sex Offender Registration and Notification Act, a “sex offense” includes any criminal offense with an element involving a sexual act or sexual contact, along with any specified offense against a minor.9Office of the Law Revision Counsel. 34 USC 20911 – Relevant Definitions, Including Amie Zyla Expansion of Sex Offense Definition That is a broad net, and it catches people convicted of offenses they may have thought of as minor, including public indecency, some misdemeanor sexual contact charges, and statutory rape in borderline age cases.
Federal law carves out one important exception. Consensual sexual conduct is not a registerable sex offense when the other person was an adult, and it is also excluded when the younger person was at least 13 and the offender was no more than four years older.9Office of the Law Revision Counsel. 34 USC 20911 – Relevant Definitions, Including Amie Zyla Expansion of Sex Offense Definition That federal floor does not stop states from imposing stricter registration requirements of their own. Many states require registration for indecent exposure convictions, and some mandate lifetime registration for certain statutory rape offenses. The registry restricts where you can live and work, and it is publicly searchable. For conduct that started as a bad decision rather than predatory behavior, registration can be the most lasting consequence of all.