Patterns of HIV transmission in the seven countries of southeastern Europe (Albania, Bosnia and Herzegovina, Croatia, Montenegro, former Yugoslav Republic of Macedonia, Serbia and Slovenia) indicate that men who have sex with men (MSM) bear the highest burden of HIV. In 2008, MSM represented 56% of all HIV cases reported in Serbia, and 71 and 76% in Slovenia and Croatia, respectively. In other countries the number of reported HIV cases attributed to MSM remains low, which is likely due to under reporting. HIV prevalence measured in surveys was the highest among MSM compared with other at-risk groups, ranging from 0.7% in Bosnia and Herzegovina to 6.1% in Serbia. Data on sexual behaviors and HIV testing uptake indicate an urgent need to increase coverage with prevention services.