In the early 1980s, Portugal could be classified as a highly endemic area for hepatitis A. However, marked economic and sanitary improvements took place during the following years. In this study we evaluated the temporal trends in the prevalence of hepatitis A in children and adolescents, to identify risk factors for the infection. The study sample included students aged 6 to 19 years (n=999), attending public and private schools. All randomly selected participants gave information on social, demographic, clinical and behavioural variables, but only 667 (67.4%) agreed to provide a blood sample for the determination of total and immunoglobulin M (IgM) anti-hepatitis A virus (HAV) antibodies. The prevalence of anti-HAV-positive subjects was 27.9%, with a linear age-related increase (r=0.87, P=0.011) from 20.9% at 6-7 years to 37.8% at 18-19 years. The crowding index and the level of maternal education were the only independent predictors of hepatitis A infection. This study showed a clear decrease in hepatitis A prevalence in our population. However, it remains a common infection in Portugal, easily acquired early in life and associated with indicators of poverty.