An evolutionary model of sexual behavior was used to generate predictions about sex differences in sexual arousal. Survey instruments were used to test these predictions with 388 adolescents, aged 12–18, from varying socioeconomic strata and geographic regions. Boys reported that their first arousal occurred at the start of puberty or before, usually in response to a visual stimulus, whereas girls generally reported first arousal as occurring 2–3 or more years after puberty, within a social/romantic context. The modal boy reported sexual arousal as occurring several times daily, the modal girl once or twice a week. Boys reported their arousal to be more discriminable, of greater intensity, and more distracting than the girls'. The sexes differed in attitudes related to sexual behavior. However, when reporting emotions and feelings coterminous with sexual arousal, the sexes did not differ. Retrospective college samples of 262 students from West Coast colleges replicated the adolescent data. A survey of 280 East Coast college students found that women's sexual arousal was significantly more partner‐dependent than men's. Results were interpreted as supporting evolutionary models of sex differences in sexuality.