The program evaluated is the Sex Offender Treatment and Evaluation Project (SOTEP), which was established by the California Department of Mental Health in 1985. SOTEP provides a comprehensive cognitive-behavioral treatment program that uses a relapse prevention framework. It is a prescriptive, multicomponent approach designed to help offenders identify factors that place them at risk of reoffending and to develop coping responses to these risks. The evaluation's research design included three groups: a treatment group, a volunteer control group (those who volunteered for but did not receive treatment), and a nonvolunteer control group (subjects who refused treatment). Although the treatment group had the lowest reoffending rates for both sex and other violent crimes, main-effects analyses did not produce conclusive results on the program's effectiveness. The results show the importance of including appropriate comparison groups, managing attrition from both treatment and methodological perspectives, examining sex and other violent offenses separately as outcome variables, using tests with adequate statistical power, and analyzing data while considering time at risk for reoffending. 1 table, 4 figures, and 46 references