Wastewater treatment workers (WWTW) are potentially exposed to a variety of infectious agents and toxic materials. We conducted a retrospective epidemiological study to examine the prevalence of infectious diseases and associated symptoms in WWTW. From a possible 242 WWTW, 150 completed a questionnaire that provided data pertaining to the diagnosis of an infectious disease or the prevalence of associated symptoms over a 12-month period. Comparison data were obtained from questionnaires completed by 54 college maintenance and oil refinery workers. The WWTW exhibited a significantly higher prevalence of gastroenteritis, gastrointestinal symptoms (specifically abdominal pain), and headaches. No significant differences were found with regard to respiratory and other symptoms. Employees classified by exposure categories did not exhibit significant differences in the prevalence of symptoms. While significant differences were found with regard to the health status of WWTW and controls, it appears that these risks are confined to symptoms and infectious diseases associated with the gastrointestinal system and are not inclusive of all such symptoms or diseases.