Associations between individual- and family-level psychosocial factors and sexual behavior were examined among 325 adolescents ages 10-18 in rural Kenya. History of sexual activity was reported by 51% of males and 30% of females. Among those reporting sex within the past year, 64% of males and 32% of females had multiple partners; 85% of males and 54% of females reported not using a condom at last sex. Multivariate logistic regression modeling demonstrated sexually active adolescents were significantly more likely to be older, male, more accepting of risky behavior, and have greater perceived HIV risk, caregiver social support, social support related to HIV, and emotional problems. Youths reporting high-risk behavior (unprotected sex or multiple partners) were significantly more likely to be younger, male, and have lower sex-related self-efficacy, lower caregiver monitoring, and more externalizing problems. Future studies should evaluate HIV prevention interventions targeting improvements in mental health and family relationships.