BACKGROUND: Recent advances in biomedical prevention strategies, including pre-exposure prophylaxis (PrEP) and achieving an undetectable viral load (UVL) among HIV-infected persons, show promise in curbing the rising incidence of HIV among men who have sex with men (MSM) in the United States. This mixed-methods study aimed to investigate the frequency with which MSM encounter potential sex partners on geosocial networking apps who disclose biomedical prevention use, and how MSM make decisions about condom use after these disclosures. METHOD: Participants were recruited through advertisements placed on a large geosocial networking app for MSM. A total of 668 and 727 participants, respectively, responded to questionnaires assessing partner disclosure of PrEP use and UVL. Each questionnaire included an open-ended item assessing reasons for condomless anal sex (CAS) with partners using biomedical prevention. RESULTS: Across both surveys, most respondents encountered potential sex partners who disclosed PrEP use or UVL, and the majority of those who met up with these partners engaged in CAS at least once. Qualitative analyses found that most participants who reported CAS did so after making a calculated risk about HIV transmission. We also describe a novel risk reduction strategy, "biomed-matching," or having CAS only when both individuals use PrEP or have UVL. We report serostatus differences in both quantitative and qualitative findings. CONCLUSIONS: Disclosure of PrEP use and UVL is not uncommon among MSM. Many MSM make accurate appraisals of the risks of CAS with biomedical prevention, and mobile apps may aid with disclosing biomedical prevention use.