We used retrospective (2012-2013) chart review to examine breast cancer screening among transgender persons and sexual minority women (n = 1263) attending an urban community health center in Massachusetts. Transgender were less likely than cisgender patients and bisexuals were less likely than heterosexuals and lesbians to adhere to mammography screening guidelines (respectively, adjusted odds ratios = 0.53 and 0.56; 95% confidence intervals = 0.31, 0.91 and 0.34, 0.92) after adjustment for sociodemographics. Enhanced cancer prevention outreach is needed among gender and sexual minorities.