This study compared male and female university students' experiences with online sexual activity (OSA) and tested a model explaining gender differences in OSA. OSAs were categorized as non-arousal (e.g., seeking sexuality information), solitary-arousal (e.g., viewing sexually explicit materials), or partnered-arousal (e.g., sharing sexual fantasies). Participants (N = 217) completed measures of OSA experience, sexual attitudes, and sexual experience. Significantly more men than women reported engaging in solitary-arousal and partnered-arousal OSA and doing so more often. However, the men and women who reported having engaged in partnered-arousal activities reported equal frequencies of experience. There were no significant gender differences for engaging in non-arousal OSA experience. These results support the importance of grouping OSAs in terms of the proposed non-arousal, solitary-arousal, and partnered-arousal categories. Attitude toward OSA but not general attitudes toward or experiences with sexuality partially mediated the relationship between gender and frequency of engaging in arousal-oriented OSA (solitary and partnered OSA). This suggests that attitude toward OSA specifically and not gender socialization more generally account for gender differences in OSA experience.