Objective: The objective of this study was to determine the epidemiology of herpes simplex virus type 2 (HSV-2) in general and socially marginalized populations of low-income, urban, coastal Peru. Study: Two low-income populations were administered an epidemiologic survey and serologic tests, determining risk behavior, HSV-2, and HIV prevalence. Results: In the socially marginalized population, HSV-2 prevalence was 72.3% in men who have sex only with men (MSOM), 42.5% in women, and 20.7% in men. In the general population, HSV-2 prevalence was 20.5% in women and 7.1% in men. In all groups except the male general population, HSV-2 prevalence increased with age or number of sexually active years (both P <0.001). HSV-2 infection was associated with HIV infection in MSOM (P <0.023) and other socially marginalized men (P <0.01). Conclusion: HSV-2 was common in both low-income populations, and control programs are needed in Peru given high prevalence and association with HIV infection. Prevention of HSV-2 infection should target individuals before they become sexually active. Copyright © 2005, American Sexually Transmitted Diseases Association All rights reserved.