Outbreaks of hepatitis A among men who have sex with men (MSM) are a recurring problem in many large cities in the industrialized world. Because MSM are at high risk for acquiring hepatitis A, in 1995 the Advisory Committee on Immunization Practices (ACIP) recommended that MSM be vaccinated against hepatitis A. These recommendations have not been implemented widely, even in outbreak settings. This report summarizes the investigation of an ongoing outbreak of hepatitis A among MSM in Atlanta, Georgia, and a public health vaccination campaign in response to the outbreak.