Emerging adults (M = 18.99 years, SD = .50) completed cross-sectional questionnaires (N = 943) and targeted follow-up telephone surveys (N = 202) across the transition to college. Gender, personal goals (dating, friendship, academic), and past sexual behavior were examined as predictors of reasons to have and not to have sex. Men rated Self-focused reasons to have sex as more important; women rated Partner-focused reasons to have sex and Ethical reasons not to have sex as more important. Importance of Pregnancy/STD reasons not to have sex did not differ by gender. Before college entrance, sexual history and personal goals predicted endorsement of reasons for/against sex. Personal goals predicted first intercourse during freshman year. Limitations of the study include the single university sample and use of closed-ended self-report measures. Personal goals and reasons for/against sex are associated with sexual behavior and should be addressed in programs designed to promote sexual health among emerging adult college students.