OBJECTIVES: In this phase I safety trial of tenofovir gel, a candidate vaginal microbicide for human immunodeficiency virus (HIV) prevention, a mixed-methods design was used to gather acceptability data among women participants. The impact of acceptability factors on use of the gel and the relationship between qualitative and quantitative acceptability data are explored. METHODS: Participants included low-risk, HIV-uninfected, and clinically stable HIV-infected women. Participants were enrolled into cohorts stratified by HIV serostatus, sexual activity, gel concentration, and frequency of use. Quantitative data were collected via interviewer-administered structured questionnaires. Qualitative data were collected via semistructured small group discussions. RESULTS: Although 94% of participants stated they would "probably" or "definitely" use tenofovir gel, a range of responses emerged on multiple domains relevant to microbicide acceptability during the qualitative discussions. Lubrication, leakage, sexual pleasure, and the possibility of covert use were central to women's qualitative assessments of tenofovir gel. CONCLUSIONS: Quantitative results indicate that tenofovir vaginal gel was acceptable to almost all users, while qualitative findings indicate that acceptability is complex, varies among users, and is likely shaped by a variety of contextual factors that manufacturers will need to consider to optimize use-effectiveness. Because of the differences in the qualitative and quantitative responses, the authors argue that future trials of candidate microbicides should include strategic collection of mixed-methods microbicide acceptability data.