The mortality and incidence of cancer in three groups of workers with occupational exposure to ethylene oxide have been assessed. Eight cases of leukemia have occurred among 733 ethylene oxide-exposed workers compared with an expected 0.8 cases. Six cases of stomach cancer have been reported compared with 0.65 cases expected. These epidemiologic results provide support for an increased risk of malignancy in individuals with extended and intermittent exposure to low concentrations of ethylene oxide.