An increased incidence of hepatitis A was observed in Naples from 1990-1991. A hospital-based case-control study was carried out to evaluate the relative importance of various risk factors. A hundred and ninety-eight cases and 238 hospital controls were recruited during the study period. The strongest association was contact with a jaundiced person among children. A correlation was also shown for children and adults with raw shellfish consumption and pre-school nursery attendance or presence in the household of children attending pre-school nurseries. History of travel and intravenous drug use were risk factors for adult subjects. Considering the relative importance of the specific risk factors we found that 38% of the acute hepatitis A cases were attributable to contact with a jaundiced person, 15% to presence in the household of children attending pre-school nurseries and 28% to raw shellfish consumption.