This article systematically reviews 75 studies that examine the prevalence of sexual assault victimization among gay or bisexual (GB) men, and lesbian or bisexual (LB) women, in the United States. All studies were published between 1989 and 2009 and report the results of quantitative research. The authors reviewed the reported prevalence of lifetime sexual assault victimization (LSA), and where available, childhood sexual assault (CSA), adult sexual assault (ASA), intimate partner sexual assault (IPSA), and hate crime-related sexual assault (HC). The studies were grouped into those that used a probability or census sampling technique (n=25) and those that used a non-probability or ''community-based'' sampling technique (n=50). A total of 139,635 gay, lesbian, and bisexual (GLB) respondents participated in the underlying studies reviewed. Prevalence estimates of LSA ranged from 15.6-85.0% for LB women and 11.8-54.0% for GB men. Considering the median estimates derived from the collective set of studies reviewed, LB women were more likely to report CSA, ASA, LSA, and IPSA than GB men, whereas GB men were more likely to report HC than LB women. Across all studies, the highest estimates reported were for LSA of LB women (85.0%), CSA of LB women (76.0%), and CSA of GB men (59.2%). With some exceptions, studies using non-probability samples reported higher sexual assault prevalence rates than did population-based or census sample studies. The challenges of assessing sexual assault victimization with GLB populations are discussed, as well as the implications for practice, policy, and future research.