This study is the first to quantify experiences of discrimination in treatment undertaken by sexual and gender minority prostate cancer patients. Participants were 192 gay and bisexual and one transgender prostate cancer patients living in the US recruited from North America's largest online cancer support group. In this online survey, discrimination in treatment was measured using the Everyday Discrimination Scale (EDS), adapted for medical settings. Almost half (46%) endorsed at least one item, including 43% that the provider did not listen, 25% that they were talked down to, 20% that they received poorer care than other patients, 19% that the provider acted as superior, and 10% that the provider appeared afraid of them. While most (26.3%) rated the discrimination as "rare" or "sometimes" (EDS=1-3), 20% reported it as more common (EDS≥4). Most attributed the discrimination to their sexual orientation, or to providers being arrogant or too pushed for time. Discrimination was significantly associated with poorer urinary, bowel, and hormonal (but not sexual) EPIC function and bother scores, and with poorer mental health (SF-12). Those who had systemic/combined treatment (versus either radiation only or surgery only) were more likely to report discrimination. This study provides the first evidence that discrimination in prostate cancer treatment, including micro-aggressions, appear a common experience for gay and bisexual patients, and may result in poorer health outcomes.