The article first discusses methodological design for evaluating sex offender treatment and then considers criteria for assessing treatment effectiveness, notably recidivism (the commission of additional sexual offenses after treatment). Various treatment modalities for sex offenders are discussed; major treatment categories are physical treatments (psychosurgery, castration, and pharmacologic interventions). Psychological treatments discussed encompass nonbehavioral approaches, cognitive/behavioral programs, institution-based programs, and outpatient programs. The author notes that previous reviews of sex offender treatment have either taken a severe methodological stance and concluded that empirical evidence is not sufficiently reliable to establish treatment effectiveness with sex offenders or have ignored methodological issues and expounded the virtues of particular treatment approaches. This article concludes that there is sufficient evidence to establish the effectiveness of some treatment programs with some offenders. Comprehensive cognitive/behavioral programs and those programs that use antiandrogens in conjunction with psychological therapy apparently offer the greatest chance of succeeding. These programs, however, do far better with child molesters and exhibitionists than with rapists. Currently, there is insufficient evidence to identify in advance those patients who will profit least (except for rapists) from treatment. 115 references