BACKGROUND: The occurrence of hepatitis A in the United States is heterogeneous because of disease cycles with substantial variation in incidence among states and involvement of numerous behavioral risk factors. In spite of the Advisory Committee on Immunization Practices' (ACIP) 1999 recommendation for routine hepatitis A immunization in states with high rates of disease and the fact that disease rates are at a historic low, outbreaks continue to occur. METHODS: We reviewed outbreaks of hepatitis A in the United States occurring from 1994 through 2004. We searched PubMed, ProMed, Google, and the CDC Foodborne Disease Outbreak and Epi-X Internet sites to ascertain the number and type of hepatitis A outbreaks. The CDC's MMWR publication and the Hepatitis Control Report were also searched. RESULTS: A total of 256 hepatitis A outbreaks were identified from 1994 through 2004. The mean number of outbreaks was 23 per year (median 25). The number of outbreaks in states with traditionally low/intermediate endemic rates of hepatitis A remained relatively constant during the study period. Outbreaks declined significantly (P = 0.01) in states with previously high rates of disease--most of which have implemented hepatitis A vaccination programs. CONCLUSIONS: Outbreaks of hepatitis A continue to occur in the United States despite the licensure of two safe and effective vaccines in 1995 and the apparent decline in the number of outbreaks in states with previously high rates of hepatitis A. The recent ACIP recommendation for universal hepatitis A vaccination at age 1 year in all states will contribute to a further reduction in hepatitis A outbreaks.