The high level of HIV infection in Kenya and most of Sub-Saharan Africa has led to an increased interest in understanding the determinants of sexual behavior among young people who form a group at high risk of infection due to their sexual behavior. In the absence of curative treatments for HIV, prevention remains the most practical weapon against the AIDS epidemic. To design effective prevention interventions, it is important to understand the dynamics and determinants of people’s sexual behavior within the cultural and social contexts where sexual encounters occur. The current study had two primary aims. First, the cross-sectional study utilized a socioecological conceptual framework to examine sociodemographic characteristics, behavioral factors, and other variables that are associated with condom use for HIV-prevention among a sample of 3612 high school students in Nairobi, Kenya. Multilevel multiple logistic regression was used to investigate the relative importance of various classes of variables in predicting actual condom use and intentions to use condoms. Overall, attitudinal factors emerged as the primary predictors of intentions to use condoms among young people with no previous sexual contacts while contextual and behavioral variables, such as engaging in risk behavior and the type of sexual partner, were the chief predictors of condom use at last intercourse for sexually experienced youth Second, the study examined factors that distinguished among different types of condom users i.e. consistent, sporadic, and nonusers because this information may aid in the development of more precisely targeted interventions. Multinomial logistic regression was used to examine what variables distinguish different groups of users. Results indicated that males who reported consistent condom use tended to have initiated sexual intercourse at an older age than sporadic condom users. Compared to nonusers, consistent users were more likely to have initiated sexual intercourse at an older age, to have greater perceptions of peer acceptance of safer sex, and to engage in risky behavior more frequently. Study findings support the need for comprehensive reproductive health programs that address the multiple factors influencing young people’s sexual behavior.