To investigate risk factors during a community outbreak of hepatitis A we carried out a case- control study of 35 cases and 49 matched controls using an interviewer-administered questionnaire on clinical history, travel, household details including domestic toilet facilities, infectious contacts, and food history. Of 99 cases notified in the city during the outbreak year, 50 (51%) were young adults age 15–34 years. Hepatitis A infection was independently associated with household contact with a case (P=0·0005), and sharing a household with children in primary school (OR 3·4, 95% CI 1·2–9·5, P=0·008) with risk increasing with number of primary-school pupils in the household (χ2 for linear trend 6·47, P=0·01). We concluded that in a population with a low prevalence of hepatitis A, adults who live in the same household as primary-school-age children are at increased risk of acquiring the infection during community outbreaks.