Municipal sewage treatment plant workers are potentially exposed to a multitude of industrial chemicals and pathogenic microorganisms. A questionnaire survey of working habits, lifestyle and symptoms of illness was conducted among 189 municipal sewage treatment plant workers processing between three and ten million gallons of wastewater daily in 16 plants in New York State between March and July of 1984. Water treatment plant workers in the same cities comprised the comparison group. Sewage workers reported a significantly higher frequency of headache, dizziness, sore throat, skin irritation and diarrhea within the month immediately preceding receipt of the questionnaire, after controlling for various possible confounders. Eye and skin irritation were significantly associated with exposure to mutagens. The health significance of these findings and possible sources of error in assessing risk are discussed.