Women rarely commit sexual crimes except as accomplices to men. The three categories of male offenders are those acting out of psychotic disorders; those who are antisocial personalities and whose sexual offenses are incidental to other crimes; and the paraphiliacs, for whom sexual motivation is the main theme of the violence. Paraphiliacs form the largest group. Their conduct includes frottage, sadism, masochism, bestiality, pedophilia, and rape. Data from paraphiliacs in outpatient treatment programs in Mississippi, Tennessee, and New York show that more than half developed their deviant arousal pattern before age 18. More than half had multiple diagnoses that overlapped a variety of paraphilias. Denial of paraphilic arousal was common, presenting dilemmas for evaluation, treatment, and interaction with the criminal justice system. Psychophysiological methods involving penile measurements are the most valid method of determining sexual interests, although these methods involve both methodological and ethical concerns. Other behavioral characteristics that should be assessed include cognitive distortions, insufficient arousal to nondeviant stimuli, deficits in assertiveness skills, and lack of sexual knowledge and function. Treatment should focus on the individual's specific excesses and deficits and may include covert desensitization or satiation. 46 references.