BACKGROUND: Recent reports of high HIV infection rates among men who have sex with men (MSM) from Asia, Africa, Latin America, and the former Soviet Union (FSU) suggest high levels of HIV transmission among MSM in low- and middle-income countries. To investigate the global epidemic of HIV among MSM and the relationship of MSM outbreaks to general populations, we conducted a comprehensive review of HIV studies among MSM in low- and middle-income countries and performed a meta-analysis of reported MSM and reproductive-age adult HIV prevalence data. METHODS AND FINDINGS: A comprehensive review of the literature was conducted using systematic methodology. Data regarding HIV prevalence and total sample size was sequestered from each of the studies that met inclusion criteria and aggregate values for each country were calculated. Pooled odds ratio (OR) estimates were stratified by factors including HIV prevalence of the country, Joint United Nations Programme on HIV/AIDS (UNAIDS)-classified level of HIV epidemic, geographic region, and whether or not injection drug users (IDUs) played a significant role in given epidemic. Pooled ORs were stratified by prevalence level; very low-prevalence countries had an overall MSM OR of 58.4 (95% CI 56.3-60.6); low-prevalence countries, 14.4 (95% CI 13.8-14.9); and medium- to high-prevalence countries, 9.6 (95% CI 9.0-10.2). Significant differences in ORs for HIV infection among MSM in were seen when comparing low- and middle-income countries; low-income countries had an OR of 7.8 (95% CI 7.2-8.4), whereas middle-income countries had an OR of 23.4 (95% CI 22.8-24.0). Stratifying the pooled ORs by whether the country had a substantial component of IDU spread resulted in an OR of 12.8 (95% CI 12.3-13.4) in countries where IDU transmission was prevalent, and 24.4 (95% CI 23.7-25.2) where it was not. By region, the OR for MSM in the Americas was 33.3 (95% CI 32.3-34.2); 18.7 (95% CI 17.7-19.7) for Asia; 3.8 (95% CI 3.3-4.3) for Africa; and 1.3 (95% CI 1.1-1.6) for the low- and middle-income countries of Europe. CONCLUSIONS: MSM have a markedly greater risk of being infected with HIV compared with general population samples from low- and middle-income countries in the Americas, Asia, and Africa. ORs for HIV infection in MSM are elevated across prevalence levels by country and decrease as general population prevalence increases, but remain 9-fold higher in medium-high prevalence settings. MSM from low- and middle-income countries are in urgent need of prevention and care, and appear to be both understudied and underserved.