Repetitive behavior is a core feature of autism spectrum disorder. We used 8-week data from two federally funded, multi-site, randomized trials with risperidone conducted by the Research Units on Pediatric Psychopharmacology Autism Network to evaluate the sensitivity of the Children's Yale-Brown Obsessive Compulsive Scale modified for autism spectrum disorder to detect change with treatment. Study 1 included 52 subjects assigned to placebo and 49 subjects to risperidone under double-blind conditions. In Study 2, 49 subjects received risperidone only and 75 subjects received risperidone plus parent training. The combined sample consisted of 187 boys and 38 girls (aged 4-17?years). At the medication-free baseline, the internal consistency on the Children's Yale-Brown Obsessive Compulsive Scale modified for autism spectrum disorder total score was excellent (Cronbach's alpha = 0.84) and the mean scores were similar across the four groups. Compared to placebo in Study 1, all three active treatment groups showed significant improvement (effect sizes: 0.74-0.88). There were no differences between active treatment groups. These results indicate that the Children's Yale-Brown Obsessive Compulsive Scale modified for autism spectrum disorder has acceptable test-retest as evidenced by the medium to high correlations in the placebo group and demonstrated sensitivity to change with treatment.