Colorectal cancer is a major public health problem in industrialised countries. Several studies have shown that social environment influences survival in cancer patients in many countries, but the causes remain unknown. In France, very little work has been done in this area. Our aim was to assess whether social environment influences survival of colorectal cancer patients in a well-defined French population and, if so, to what extent this could be explained by differences in stage at diagnosis or in treatment. The study population consisted of 1,642 colorectal cancer patients diagnosed between 1978 and 1987 in the French department of Calvados. Socio-demographic characteristics were assessed in terms of socio-professional category, place of residence (urban vs. rural) and distance from the place of residence to a specialised health-care centre. The relation between social environment, clinical factors and survival was studied using 2 multivariate methods (Cox model and relative survival method). Patients with poorer prognosis were found to be farmers of both sexes and individuals without occupation among males. Differences in survival were not explained entirely even when variations in stage at diagnosis and in treatment were taken into account.