The cancer morbidity in a large group of male German agricultural workers exposed to pesticides was investigated through a retrospective cohort study. A total of 169 malignant tumors were diagnosed in 1658 men who began to work with pesticides between 1948 and 1972, and who continued this type of activity for at least 5 yr. The SMR (standardized mortality ratio) of 2.0 for lung cancer morbidity (mortality) in these pesticide‐exposed subjects was significantly higher than that for the general male population of the German Democratic Republic. A positive correlation between the duration of employment and the mortality due to lung cancer (mainly undifferentiated and small‐cell carcinomas) suggested a dose‐effect relation. The smoking habits of the exposed men did not differ from those of the general male population of the German Democratic Republic. Because the subjects had been exposed to many different substances, the study does not permit any conclusions to be drawn in respect to the carcinogenicity of individual pesticides. The increased mortality due to lung cancer is presumably the result of an additive effect of different pesticide ingredients or of by‐products whose carcinogenic effect has been definitely or tentatively established through experimental or epidemiologic studies (e.g., arsenic, asbestos, chlorinated dibenzodioxins, DDT). The results of the present investigation emphasize the need for effective measures to protect workers during occupational contact with pesticides.