Abstract Hepatitis A is a viral disease with a significant public health impact, especially in developing countries. Improvements in sewage services could prevent hepatitis A virus (HAV) dissemination into the environment and minimize the risk of infection. The aim of this study was to monitor HAV for one year in urban sewage samples from the largest wastewater treatment plant in Rio de Janeiro, Brazil to assess environmental contamination with HAV and its dissemination after treatment by an activated sludge process. For this purpose, 48 samples (24 raw sewage samples and 24 treated effluent samples) were collected from August 2009 to July 2010 for HAV detection. Using quantitative real-time PCR 14 (58%) raw sewage samples were positive for HAV, and the highest viral genome loads were detected in the spring and summer. HAV was not detected in treated effluent samples, which suggests that the viral loads observed could be easily removed by the activated sludge process, thus preventing the dissemination of HAV into the environment. All of the HAV strains sequenced belonged to subgenotype IA, which clustered closely with Brazilian and Argentine HAV strains. These data demonstrate that environmental monitoring can be a useful tool in epidemiological studies.