Few studies have examined gender-specific factors associated with the nonuse of condoms among homeless and runaway youths (HRYs)-a population at high risk for HIV infection. In this article, we evaluate these factors and explore gender differences in background experiences, psychosocial functioning, and risk behaviors among HRYs from four U.S. metropolitan areas. Of 879 sexually active HRYs sampled, approximately 70% reported unprotected sexual intercourse during a 6-month period, and nearly a quarter reported never using condoms in the same period. Among males and females, having only one sex partner in the previous 6 months had the strongest association with nonuse of condoms. Among males, nonuse was also associated with having ever caused pregnancy, frequent marijuana use, prior physical victimization, and low self-control and sociability. Among females, nonuse was associated with knowledge of HIV status, prior sexual victimization, low social support, and infrequent marijuana use. These findings highlight the ongoing need for HIV prevention services for HRYs. Implications for the scope and content of these services are discussed.