521 U.S. 346 (1997)
A state may confine a person after their sentence ends if a mental abnormality makes them dangerous. That is civil, not a second punishment.
Good law. Still followed. Later cases may have narrowed it — see Scope. Binds every court in the country on the federal question it decides.
Kansas sought to commit Leroy Hendricks, a man with a long record of sex offenses who had served his full prison sentence, under its Sexually Violent Predator Act. The Act allowed indefinite confinement on a finding of a “mental abnormality” or personality disorder making the person likely to reoffend.
The Court upheld the Act. Because commitment turns on a present mental condition and dangerousness rather than on the original crime, the Act is civil, not punitive — so it did not violate double jeopardy or the Ex Post Facto Clause, even though Hendricks had already completed his sentence.
Hendricks is what makes sexually-violent-predator commitment possible. Around twenty states and the federal government now have such laws. Its method — asking first whether the legislature meant a law to be civil, then whether it is so punitive in effect that the label fails — became the test the Court later used for registration in Smith v. Doe.
It did not say how much loss of control must be proven; Kansas v. Crane answered that. It did not approve commitment with no treatment at all or with conditions that look like prison, and later challenges focus on exactly those conditions.
Last verified against the sources above on September 30, 2026.
These are plain-language summaries of court decisions, written for general education. A ruling binds only the courts beneath the court that issued it, later decisions and new laws can change what it means, and how it applies to any one person depends on facts a summary cannot capture. Read the opinion itself, and talk to a lawyer licensed in your state before relying on any case. This page is not legal advice.