Data on cancer morbidity by occupation are available from surveillance systems, such as linkage studies based on census data and cancer register data. These data serve various purposes. First, they show the social distributions of cancer diseases. Second, they can form the background for generating hypotheses about chemical carcinogens by identifying occupations at high risk of cancer. Third, cancer morbidity data can be used in the interpretation of results from hypothesis-testing studies. Fourth, the data can facilitate the identification of cancer risks associated with new technologies and way of life in the service society. Finally, the data can be considered for inference about future trends in cancer mortality. Data from the Danish occupational cancer study are used for illustration.