This study assessed the prevalence, level of disclosure, and interpretations of sexual activities in a sample of 123 college-aged blood donors in Montreal, Quebec. Within six months of their donation, participants completed an anonymous questionnaire designed to assess sexual definitions, levels of disclosure to sexual partners, as well as prevalence of various blood safety behavioural risks. Responses indicated that (1) there was a lack of consensus regarding what constitutes 'sex', (2) levels of sexual disclosure varied widely, and (3) participants engaged in numerous blood safety behavioural risk activities. These results are discussed with respect to their implications for how people think about sex, particularly in the blood donation context. Suggestions to improve specific blood donor screening questions are also presented.