This study investigated the effects of a Men as Allies--based intervention on high school students' rape-supportive attitudes and behaviors. As hypothesized at posttest, the male and female experimental groups demonstrated a significant decrease in rape-supportive attitudes, which was maintained at follow-up. Male participants viewed peers' attitudes toward sexual violence as significantly different (worse) from peers' pretest self-ratings; after intervention, male and female experimental group participants' peer ratings were significantly more accurate.