Current research examining the effectiveness of sex offender treatment is encouraging. Despite this optimism, research focusing on men who sexually assault adult women is less optimistic. This study examines the preliminary results of 74 rapists admitted into the Phoenix program, a voluntary sex offender treatment program in a forensic psychiatric hospital. Patients were categorized according to whether they completed treatment or not. Treated rapists (n = 36) reoffended at a substantially lower rate than untreated rapists who were assessed but not treated (n = 38). Statistically significant differences in reoffense rates were found for violent, nonsexual offenses as well as nonviolent, nonsexual offenses. Although nearly twice as many treatment noncompleters reoffended sexually, the difference between the two groups was not statistically significant. Mean follow-up time was well over four years for both groups. The implications of these findings are discussed.