Hepatitis A is a significant health problem in day care centers, causing outbreaks that average 12 cases in size and three months in duration. These outbreaks have three characteristic features: children have mild or asymptomatic infections; adults (primarily parents) are the major group with clinical hepatitis; and persons having contact with one- or two-year-old children run the highest risk of infection. Outbreaks are commonest in centers that are large, have long operating hours, and enroll children younger than the age of two years (i.e., those in diapers). The presence of such children is necessary for the rapid spread of the disease. Nationally, outbreaks occur primarily in areas with many infant/toddler centers, which often form the focus for epidemics. Prevention relies on hygiene, especially hand washing. Disease control depends on early detection of outbreaks and aggressive use of immunoglobulin. The spread of hepatitis B has not been documented in day care centers; however, when a child carrying hepatitis B virus enrolls in a center, a low risk of transmission may exist and precautions are recommended, with a focus on personal hygiene.