The U.S. Supreme Court recently found the Kansas sexual predator statute constitutional. This statute permits the confinement, in mental hospitals, of sex offenders after the completion of their criminal sentences if they have a mental abnormality that might lead to future dangerous behavior. The broad definition of mental abnormality, includes both serious disorders and personality disorders that may reflect only antisocial traits, coupled with the fact that past behavior which occurred years before, is an adequate predicate for confinement. This represents a significant expansion of traditional civil commitment and a blurring of the boundaries of mental illness and deviance. The costs for this confinement are three to four times the cost of customary civil commitment and compete with costs for treatment of the seriously mentally ill.