Objectives: The study analyzed the dating and premarital sexual behaviors of adolescents with different backgrounds who had ever made friends on the Internet. The study also aimed to discern the differing influential factors on the dating and premarital sexual behavior of adolescents of the opposite sex who first met virtually or in-person. Methods: A stratified cluster sampling method was used to identify 1003 second-year public junior high school, high school, and vocational school students in Taipei with Internet friend-making experience. Participants completed a cross-sectional questionnaire. Results: Of the participants, 19.2% had dated a person of the opposite sex first met on the Internet, which was reflected in their lower score for the family relationship portion of the questionnaire (p<.001). The main factor influencing the pursuit of a virtual or reality-based romantic relationship varied with participants; those inclined to a virtual route were influenced by their friendship with opposite gender peers, while the degree of premarital sexual behavior acceptance influenced reality-based relationships (p<.001). The degree of willingness to date was the strongest predictive factor for sexual openness with Internet companions, while acceptance of premarital sexual behavior most strongly predicted pursuit of a reality-based relationship. Conclusions: Family relationship is an important protective factor to reduce high-risk sexual behavior of adolescents. The patterns of adolescent dating and premarital sexual behavior with opposite sex companions first met through the Internet and in person are different. Intervention strategies should take into account these different patterns. necessary to divide groups in designing the intervention courses to meet their different needs.