Since 1975 the U.S. Environmental Protection Agency has sponsored 11 epidemiological studies of the potential health effects associated with the treatment and disposal of sewage and sewage sludge. Three of these have been occupational exposure studies: One of sewage treatment plant employees, one of irrigation workers, and one of sludge composting workers. Four studies have involved populations living in the vicinity of activated sludge sewage treatment plants. Three studies concerned land application of wastewater for agricultural purposes, and the final study was of farm families utilizing digested sewage sludge on cropland. The design, results, interpretations, conclusions and costs of these studies are reviewed and discussed. Final analyses on two of the studies have not yet been completed. The preponderance of data was negative, but this has to be viewed with respect to the inherent problems in quantifying exposure of the involved populations and the absence of a clear end point for measuring an effect.