We explored the use of qualitative interviews to discuss discrepancies between two sources of information on unprotected sex: biomarker results and self-reported survey data. The study context was a randomized trial in Kingston, Jamaica examining the effect of STI counseling messages on recent sexual behavior using prostate-specific antigen (PSA) as the primary study outcome. Twenty women were interviewed. Eleven participants were selected because they tested positive for PSA indicating recent semen exposure, yet reported no unprotected sex in a quantitative survey ("discordant"): 5 reported abstinence and 6 reported condom use. Nine participants who also tested positive for PSA but reported unprotected sex in the survey were interviewed for comparison ("concordant"). Qualitative interviews with 6 of the 11 discordant participants provided possible explanations for their PSA test results, and 5 of those were prompted by direct discussion of those results. Rapid PSA testing combined with qualitative interviews provides a novel tool for investigating and complementing self-reported sexual behavior.