The study found that homeless youths' experience of stigma played a major role in their mental health status and level of suicide risk. These findings emphasize the importance of interventions that address social stigma as it is perceived and experienced by these youth, as well as how these perceptions affect their mental health in various domains. Treatment should focus on ways for homeless youth to replace internalized messages of guilt and shame with a more positive understanding of the various factors that underlie stigma for some groups, including gay, lesbian, bisexual, and transgendered persons, youth involved in the sex trade, and how perceptions of stigma change over time as youth are exposed to ongoing discrimination. The youth who participated in the study (n=280) were drawn from agencies and the streets of New York City and Toronto, Canada. Street interviews were conducted in a range of locations where homeless youths congregated and/or panhandled. One hundred youths were interviewed in New York and 108 in Toronto. In order to be selected for the study, youth had to be 24 years old or younger and must have had no fixed address or were living in a shelter at the time of the survey. Demographic data addressed gender, ethnicity, and sexual orientation. Information was also obtained on primary means of subsistence. A 12-item survey on social stigma experiences was developed from 7 adapted items derived from an inventory designed for persons with HIV and 5 items developed from previous qualitative work in which youth described their experiences of social stigma. Other variables measured were self-esteem, loneliness, feeling trapped, hopelessness, helplessness, and suicidal thoughts. 3 tables and 53 references