A cross-sectional survey of the seroprevalence of hepatitis A virus (HAV), B (HBV), C (HCV), and E (HEV) antibodies in a healthy population in Leon, Nicaragua was conducted and associated with demographic data. The overall prevalence of antibodies to HAV was 94.6%, to HBV 6.5% and to HEV between 4.6% and 8.0%, whereas none of 399 tested subjects showed confirmed seropositivity to HCV. A high HAV seropositivity rate (72.7%) was observed even in the lowest age groups tested (2-4 years of age). In contrast, HBV and HEV seropositivity was observed mainly in adults, the seroprevalence in > 40-year-old individuals being 15.4% and 17.6%, respectively. The overall mean hepatitis B surface antigen carrier rate was estimated to be 0.9%, and in individuals more than 20 years of age, 2.0%. The prevalence of anti-HAV as well as anti-HEV was significantly higher in people having their water supply outside rather than inside the house. Furthermore anti-HAV seroprevalence correlated with lack of access to a flush toilet. Hepatitis B virus seropositivity was more frequent in people living in a crowded environment than in those living with few household members. These findings indicate that hepatitis A is a childhood infection in Nicaragua and that the spread of the infection is facilitated by poor socioeconomic conditions. In contrast, HBV infection is relatively infrequent in the country and HCV seems to be very uncommon. Hepatitis E virus infection may occur in all age groups and is apparently associated with water-borne transmission.