Approximately 1.1 million persons in the United States are living with human immunodeficiency virus (HIV) infection. More than half of those infected are men who have sex with men (MSM). June-December 2008. The National HIV Behavioral Surveillance (NHBS) System collects risk behavior data from three populations at high risk for HIV infection: MSM, injection-drug users, and heterosexual adults at increased risk for HIV infection. Data for NHBS are collected in rotating cycles. NHBS participants must be aged ≥18 years, live in a participating metropolitan statistical area, and be able to complete a behavioral survey in English or Spanish. Men who reported being infected with HIV or who had no male sex partners during the past 12 months were excluded from this analysis. This report summarizes data gathered from 8,175 MSM during the second data collection cycle of NHBS. In addition to having at least one male sex partner, 14% of participants had at least one female sex partner during the past 12 months. Unprotected anal intercourse with a male partner was reported by 54% of the participants; 37% reported having unprotected anal sex with a main male partner (someone with whom the participant had sex and to whom he felt most committed, such as a boyfriend, spouse, significant other, or life partner), and 25% reported having unprotected anal sex with a casual male partner (someone with whom the participant had sex but with whom he did not feel committed, did not know very well, or had sex with in exchange for something such as money or drugs). Noninjection drug use during the past 12 months was reported by 46% of participants. Specifically, 38% used marijuana, 18% cocaine, 13% poppers (amyl nitrate), and 11% ecstasy. Two percent of the participants reported injecting drugs for nonmedical purposes in the past 12 months. Of the participants surveyed, 90% had been tested for HIV during their lifetime, 62% had been tested during the past 12 months, 51% had received a hepatitis vaccination, 35% had been tested for syphilis during the past 12 months, and 18% had participated in an individual- or group-level HIV behavioral intervention. MSM in the United States continue to engage in sexual and drug-use behaviors that increase the risk for HIV infection. Although many MSM had been tested for HIV infection, many had not received hepatitis vaccinations or syphilis testing, and only a small proportion had recently participated in a behavioral intervention. To reduce HIV infection among MSM, additional effort is needed to decrease the number of men who are engaging in risk behaviors while increasing the number who recently have been tested for HIV. The National HIV/AIDS Strategy for the United States delineates a coordinated response to reduce infections and HIV-related health disparities among MSM and other disproportionately affected groups. NHBS data can be used to monitor progress toward the goals of the national strategy and to guide national and local planning efforts to maximize the impact of HIV prevention programs.