OBJECTIVE: Evaluate sexual dysfunction, as measured by the Arizona Sexual Experience Scale (ASEX), in olanzapine-, quetiapine-, and risperidone-treated outpatients with schizophrenia or schizoaffective disorder. METHOD: The sexual functioning of 238 outpatients (age> or =18 years) with diagnoses of schizophrenia or schizoaffective disorder who took quetiapine (n=57), olanzapine (n=94), or risperidone (n=87) was evaluated with a one-time rating of the ASEX. The dose range for each treatment group was 5 to 40 mg/day (M=16.6 mg/day, SD=7.4) for olanzapine; 1 to 8 mg/day (M=3.9 mg/day, SD=1.6) for risperidone; and 50 to 900 mg/day (M=376.8 mg/day, SD=213.4) for quetiapine. Antipsychotic group designation was based on medication treatment at study entry (i.e., non-random assignment). Participant characteristics were collected to test for treatment group differences and for potential associations with severity of sexual dysfunction. The primary data analysis was a mixed linear model analysis of covariance with age, gender, and presence/absence of antidepressant known to cause sexual dysfunction included as covariates. RESULTS: There was a significant treatment effect on severity of sexual dysfunction, as measured by ASEX total scores (p=.04). The adjusted average ASEX total scores were lower in the quetiapine (M=17.80) than in the risperidone (M=19.69) or olanzapine (M=20.34) groups. Individual comparisons of the treatments on adjusted average ASEX total scores indicated a significant difference between olanzapine and quetiapine (p=.04), but no difference between risperidone and quetiapine (p=.17) or olanzapine and risperidone (p=.76). CONCLUSIONS: Quetiapine was associated with less severe sexual dysfunction than olanzapine and risperidone (albeit the effect between risperidone and quetiapine was not statistically significant). Olanzapine and risperidone were associated with a comparable degree of sexual dysfunction. Patients in all three treatment groups, nonetheless, experienced a moderately high degree of sexual dysfunction. Because the patients were not randomized, conclusions must be interpreted within the context of the quasi-experimental design.