Data were collected from personal interviews with 640 shelter and 600 street youths in 1992. Logistic regression analysis revealed that, after controlling for key demographic characteristics, youths who had used substances (particularly sedatives, hallucinogens, and inhalants) were much more likely than those who had not used substances to have ever attempted suicide. In addition, after controlling for their own substance use, youths with family members who had used substances were twice as likely as those without such family members to have ever attempted suicide. Study findings demonstrate the importance of developing and focusing suicide prevention efforts on RHY known to have used substances and to have substance-using family members. Recommendations are offered for the RHY service community that focus on the need for effective shelter and street outreach programs to evaluate juvenile suicide potential and histories of youth and familial substance use. 19 references and 6 tables