Introduction Most studies among sewage workers of wastewater treatment plants (WWTPs) have found a higher prevalence of gastrointestinal symptoms than among non-sewage exposed workers. Waterborne transmission of Helicobacter pylori ( H pylori ) has been hypothesised, as the bacteria can survive into an aqueous environment and has been detected in sewage. A health and hygiene questionnaire has demonstrated a higher prevalence of peptic ulcers among Belgian WWTP operators and maintenance workers than among non-sewage exposed colleagues. Objectives To assess the seroprevalence of H pylori infection in Belgian sewage workers at municipal WWTPs, and to determine whether sewage exposure is an important risk factor for acquisition of H pylori and the possible association with gastrointestinal symptoms. Methods A seroprevalence study of H pylori antibodies was conducted among 317 WWTP employees (operators, maintenance workers, laboratory personnel, other job). Information about demographic variables, possible H pylori risk factors, working history, and history of current gastrointestinal symptoms during last 3 months was obtained by a questionnaire. The presence of H pylori IgG was investigated with an ELISA. The results were compared with those of 250 employees of a pharmaceutical company (operators, maintenance workers, laboratory personnel). Results The prevalence of H pylori IgG antibodies among sewage workers was 16.7% (95% CI 12.6 to 20.8%) compared to 13.6% (95% CI 9.4 to 17.8%) among the control group. In a logistic regression model with controlling for age and educational levels, OR study/control group was 1.02 (95% CI 0.58 to 1.80 with p=0.93). No significant associations were found between the H pylori status and gastrointestinal symptoms, occupational exposures in different tasks, nor with hygienic practices. Conclusions Our results do not suggest that H pylori infection is a probable cause of part of gastrointestinal symptoms among Flemish municipal sewage workers of WWTPs.