Adolescents comprise approximately 15% of new HIV infections in Kenya. Impoverished living conditions in informal settlements place residents at high risk for HIV infection. We assessed factors associated with HIV infection among adolescents residing in urban informal settlements in Kisumu. We recruited 3,061 adolescent boys and girls aged 15-19. HIV prevalence was 2.5% overall, all newly identified cases were among girls and infection was positively associated with not completing a secondary education (p < .001). Girls who had ever been pregnant (p < .001) or out-of-school without completing a secondary education (p < .001) were more likely to be HIV-positive. Our findings of higher HIV prevalence among adolescent girls who had been pregnant or did not complete secondary school highlight the need to facilitate access to HIV testing, HIV pre-exposure prophylaxis, and sexual and reproductive health services as components of a comprehensive prevention strategy to decrease HIV infections in this priority population.