Abstract This study was designed to explore the factors that differentiate sexually experienced teenagers who become pregnant from those who do not. The study examined the differences between pregnant and never-pregnant female adolescents in personal background characteristics, family characteristics, substance use, contraceptive attitude, contraceptive knowledge, contraceptive self-efficacy, sexual history, and effective contraceptive use. Sexually experienced but never-pregnant female adolescents were selected from two vocational high schools. Pregnant adolescents were recruited by convenience sampling from obstetric clinics and health stations in Tainan City, Taiwan. Multiple logistic regression analysis identified six factors associated with pregnancy: poor contraceptive knowledge, poor contraceptive self-efficacy, low socioeconomic status, low effective contraceptive use scores, more frequent sexual intercourse, and older age. The results of this study provide health professionals with information to develop more-effective prevention and intervention programs to reduce adolescent pregnancy. The results also could be used as a reference for related research and policy development in other countries.