The 6-3 ruling reverses course from a ruling 17 years ago that states could punish homosexuals for what such laws historically called deviant sex.

Laws forbidding homosexual sex, once universal, now are rare. Those on the books are rarely enforced but underpin other kinds of discrimination, lawyers for two Texas men had argued to the court.

The men "are entitled to respect for their private lives," Kennedy wrote.

"The state cannot demean their existence or control their destiny by making their private sexual conduct a crime," he said.

Justices John Paul Stevens, David Souter, Ruth Bader Ginsburg and Stephen Breyer agreed with Kennedy in full. Justice Sandra Day O'Connor agreed with the outcome of the case but not all of Kennedy's rationale.

Chief Justice William H. Rehnquist and Justices Antonin Scalia and Clarence Thomas dissented.

"The court has largely signed on to the so-called homosexual agenda," Scalia wrote for the three. He took the unusual step of reading his dissent from the bench.

"The court has taken sides in the culture war," Scalia said, adding that he has "nothing against homosexuals."

The two men at the heart of the case, John Geddes Lawrence and Tyron Garner, have retreated from public view. They were each fined $200 and spent a night in jail for the misdemeanor sex charge in 1998.

The case began when a neighbor with a grudge faked a distress call to police, telling them that a man was "going crazy" in Lawrence's apartment. Police went to the apartment, pushed open the door and found the two men having anal sex.

As recently as 1960, every state had an anti-sodomy law. In 37 states, the statutes have been repealed by lawmakers or blocked by state courts.

Of the 13 states with sodomy laws, four -- Texas, Kansas, Oklahoma and Missouri -- prohibit oral and anal sex between same-sex couples. The other nine ban consensual sodomy for everyone: Alabama, Florida, Idaho, Louisiana, Mississippi, North Carolina, South Carolina, Utah and Virginia.

Thursday's ruling apparently invalidates those laws as well.

The Supreme Court was widely criticized 17 years ago when it upheld an antisodomy law similar to Texas'. The ruling became a rallying point for gay activists.

Of the nine justices who ruled on the 1986 case, only three remain on the court. Rehnquist was in the majority in that case -- Bowers v. Hardwick -- as was O'Connor. Stevens dissented.

A long list of legal and medical groups joined gay rights and human rights supporters in backing the Texas men. Many friend-of-the-court briefs argued that times have changed since 1986, and that the court should catch up.

At the time of the court's earlier ruling, 24 states criminalized such behavior. States that have since repealed the laws include Georgia, where the 1986 case arose.

Texas defended its sodomy law as in keeping with the state's interest in protecting marriage and child-rearing. Homosexual sodomy, the state argued in legal papers, "has nothing to do with marriage or conception or parenthood and it is not on a par with these sacred choices."

The state had urged the court to draw a constitutional line "at the threshold of the marital bedroom."

Although Texas itself did not make the argument, some of the state's supporters told the justices in friend-of-the-court filings that invalidating sodomy laws could take the court down the path of allowing same-sex marriage.

The case is Lawrence v. Texas, 02-102.