Non-gay-identifying men who have sex with men are at risk for human immunodeficiency virus (HIV) infection. To understand these men and to develop interventions to reduce their HIV risks, the authors interviewed staff at agencies that serve non-gay-identifying men who have sex with men, business people who interact with them, and the men themselves. Interviews were augmented with focus groups of non-gay-identifying men who have sex with men and field observations at sites identified as places where they meet to negotiate or have sex. These qualitative data suggested 73 possible groups, which were consolidated into 16 broader "sectors," and then formally ranked by level of HIV risk, ease of access to the sector, psychosocial risks, and influence of other local interventions or research activities. The authors identified six priority groups of non-gay-identifying men who have sex with men (and sites where members of these groups could be approached): hustlers, closeted men, experimenters, incarcerated or formerly incarcerated men, men of color, and heterosexually identified bisexuals. Masturbation and oral sex were reportedly common, but anal and vaginal sex were also noted; condom use was rarely reported. Risk behaviors among non-gay-identifying men who have sex with men persist for a variety of reasons and may require a variety of intervention approaches.