Improvement of health care policy requires an assessment of health care practices. In France, morbidity registries might be the best tool of such an assessment. This study shows how the treatment of colorectal cancer can be assessed by French cancer registries. Two studies were conducted. One cross-sectional on data from 7 cancer registries in 1990 and one longitudinal on data from 2 digestive cancer registries (departments of Calvados and Côte-d'Or) between 1978 and 1990. Cancer resection rate significantly increased from 1978 to 1990. In 1990, mean resection rate was 85%, higher for colon (89%) than rectum (79%). Sphincter preservation rate also significantly increased to 40.8% in 1990. No geographical variations were observed for surgical practices. The use of adjuvant radiotherapy had significantly increased between 1978 and 1990, more rapidly in university centres. In more recent years, the use of radiotherapy concerned 50% of resected rectal cancers without differences between the different types of health care centre. However, in 1990, great geographical variations were observed in the use of adjuvant radiotherapy. Similar geographical variations were observed for the use of chemotherapy which did not increased with time. Colorectal cancers were diagnosed more and more earlier from 1978 to 1990 in both departments of Calvados and Côte-d'Or. The French network of French cancer registries (FRANCIM) provides accurate and reliable knowledge on medical practices, geographical variations and trends. Information is also available on prognosis in cancer patients. Potentialities of cancer registries are not actually well known although such information is required to plan health care policy.