Biases associated with volunteering for studies in human sexuality were studied. Beginning with a sample of over 1000 introductory psychology students, subjects participated in a two-phase study in which those willing and unwilling to volunteer for a variety of sexuality studies were compared. In both phases of this study, volunteers were significantly different from nonvolunteers on some, but not all, dimensions assessed. Specifically, compared to nonvolunteers, volunteers reported a more positive attitude towards sexuality, less sexual guilt, and more sexual experience. These differences were independent of subject gender. Sobering implications of these findings for the generalizability of sexuality research results are discussed.