Objectives: To review current approaches to HIV surveillance among men who have sex with men (MSM), identify illustrative best practices and lessons learned, and outline ways to enhance surveillance systems. Methods: Review of the literature and institutional guidelines for HIV/AIDS, sexually transmitted infection (STI), and behavioral surveillance and summary of results of an international workshop. Results: On-going formative research, HIV/AIDS and STI case reporting, HIV prevalence and incidence studies, and behavioral surveys are essential components of an effective HIV surveillance system for MSM. Alliances with key organizations and actors in MSM communities provide points of access, assist in the development of measures, and guide appropriate use of data. Sampling techniques (convenience, snowball, quota, microsite, time-location, and population-based) offering a range of methods, complexity, and cost have been successfully implemented in MSM communities. Plausible estimates of the size of MSM populations, which are ultimately crucial to the interpretation of surveillance data, can be improved upon using primary and secondary data. Conclusions: The purpose of HIV surveillance among MSM is not only to monitor disease occurrence and its antecedents, but to regularly use data to plan and evaluate prevention and care programs, advocate for prevention resources, and improve the health, social welfare and human rights of MSM. Practical, incremental steps can be taken to improve HIV surveillance among MSM in all regions of the world in all stages of the epidemic. © 2001 Lippincott Williams & Wilkins.