This study explores premarital sex among adolescents and its health outcomes in a typical East Asian society, Taiwan. As a collective society in terms of cultural heritage, a particular target of this study was perceived peer pressure and its contextual influence. The data were taken from the Taiwan Youth Project, 2004 and 2007, and never married youth aged 20 years constituted our sample (N=3530). Best friends' sexual behavior and other context-related factors, such as school attendance and community participation, are presumed to influence adolescent premarital sex as well as their health status. Logistic regression models show a positive and significant association between the perception of friends' sexual behavior and the likelihood of adolescent premarital sex engagement, after adjusting for the youth's own sex-related experience and attitudes, individual characteristics, and family background. The analysis also confirms that school attendance and community participation are significantly associated with a lower likelihood of having premarital sex. Furthermore, adolescent premarital sex was found to be linked to the perceived health status of the youth (self-rated health, smoking, and drinking), as expected. These findings demonstrate the importance of peers and social context, which suggests that HIV prevention and health promotion programs for youth need to take friendship networks and social context into consideration.