This study examined the relationship between adolescents' beliefs about the prevalence of youth suicide ideation (ideation descriptive norms) and suicide attempts (attempt descriptive norms) with self-reported suicide ideation and attempts. Descriptive norms, suicide ideation, and suicide attempts as well as gender, race/ethnicity, and exposure to family, peer, and others' suicide were assessed in 2,109 students at six suburban New York State high schools. After controlling for demographic variables and exposure to suicide, elevated ideation descriptive norms and attempt descriptive norms were associated with higher rates of suicide ideation and lifetime suicide attempts among adolescents. Adolescents who believed suicide ideation and attempts to be more widespread among peers (i.e., elevated ideation and attempt descriptive norms) were more likely to endorse suicide ideation and attempts. Correcting these descriptive norms may be a worthwhile goal for school-based suicide prevention programs.