A case-control study based on 28 serologically confirmed cases of hepatitis A and 42 home contacts with no recent or past evidence of hepatitis A virus (HAV) infection was conducted to determine the importance of shellfish exposure in the transmission of HAV during a non-epidemic period in Singapore. It was found that consumption of partially-cooked cockles (Anadara granosa) was significantly associated with the illness (p less than 0.001). No other types of locally available shellfish including oysters, mussels and clams were incriminated. The public should be constantly reminded to refrain from consuming raw and inadequately cooked bivalve molluscs all the time, and not just during epidemics.