The authors evaluated emotional distress among 9th-12th grade students, and examined whether the association between being lesbian, gay, bisexual, and/or transgendered (i.e., "LGBT") and emotional distress was mediated by perceptions of having been treated badly or discriminated against because others thought they were gay or lesbian. Data come from a school-based survey in Boston, Massachusetts (n = 1,032); 10% were LGBT, 58% were female, and ages ranged from 13 to 19 years. About 45% were Black, 31% were Hispanic, and 14% were White. LGBT youth scored significantly higher on the scale of depressive symptomatology. They were also more likely than heterosexual, non-transgendered youth to report suicidal ideation (30% vs. 6%, p < 0.0001) and self-harm (21% vs. 6%, p < 0.0001). Mediation analyses showed that perceived discrimination accounted for increased depressive symptomatology among LGBT males and females, and accounted for an elevated risk of self-harm and suicidal ideation among LGBT males. Perceived discrimination is a likely contributor to emotional distress among LGBT youth.