In a multi-site study of vaginal microbicide acceptability conducted with sexually active young women, quantitative assessments revealed significant differences in acceptability by site. Participants in Puerto Rico rated the gel more favourably than mainland US participants in terms of liking the gel and likelihood of future use. To explain these differences, we examined responses to qualitative behavioural assessments. Young women in mainland USA associated gel leakage with uncomfortable sensations experienced during menstruation, while young women in Puerto Rico had positive associations of gel use with douching. These negative or positive associations affected assessments of the gel's physical qualities. In addition, young women's perceptions of primary partners' support for microbicide use influenced sexual satisfaction with the gel and, ultimately, product acceptability. Finally, geographic HIV-risk context contributed to heightened HIV-risk perception, which influenced likelihood of future microbicide use, even for women in stated monogamous relationships. Future microbicide acceptability studies should take into account potential differences in acceptability by site such as HIV-risk perception based on local HIV prevalence, popularity of vaginal hygiene products in a specific area and male attitudes in different cultures concerning women's use of HIV protection strategies.