358
Opinion of the Court
pacitated. As we have recognized, "[p]revious instances of violent behavior are an important indicator of future violent tendencies." Heller v. Doe, 509 U. S. 312, 323 (1993); see also Schall v. Martin, 467 U. S. 253, 278 (1984) (explaining that "from a legal point of view there is nothing inherently unattainable about a prediction of future criminal conduct").
A finding of dangerousness, standing alone, is ordinarily not a sufficient ground upon which to justify indefinite involuntary commitment. We have sustained civil commitment statutes when they have coupled proof of dangerousness with the proof of some additional factor, such as a "mental illness" or "mental abnormality." See, e. g., Heller, supra, at 314-315 (Kentucky statute permitting commitment of "mentally retarded" or "mentally ill" and dangerous individual); Allen v. Illinois, 478 U. S. 364, 366 (1986) (Illinois statute permitting commitment of "mentally ill" and dangerous individual); Minnesota ex rel. Pearson v. Probate Court of Ramsey Cty., 309 U. S. 270, 271-272 (1940) (Minnesota statute permitting commitment of dangerous individual with "psychopathic personality"). These added statutory requirements serve to limit involuntary civil confinement to those who suffer from a volitional impairment rendering them dangerous beyond their control. The Kansas Act is plainly of a kind with these other civil commitment statutes: It requires a finding of future dangerousness, and then links that finding to the existence of a "mental abnormality" or "personality disorder" that makes it difficult, if not impossible, for the person to control his dangerous behavior. Kan. Stat. Ann. § 59-29a02(b) (1994). The precommitment requirement of a "mental abnormality" or "personality disorder" is consistent with the requirements of these other statutes that we have upheld in that it narrows the class of persons eligible for confinement to those who are unable to control their dangerousness.
Hendricks nonetheless argues that our earlier cases dictate a finding of "mental illness" as a prerequisite for civil commitment, citing Foucha and Addington. He then as-
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