The effectiveness of adjuvant radiotherapy (ART) in the treatment of rectal cancer (RC) is established for the local control of the tumor, but doubt remains as concerns improvement in survival. The aim of this work was to assess the present techniques and trends of ART in a French department based on a population-based study. From 1978 to 1986, 616 cases of RC were diagnosed in the department of Calvados (France). Tumor was removed in 346 patients (56 percent). Of these 346 cases, 29 percent were irradiated, 3/4 postoperatively and one forth preoperatively. Besides sex and age, the type of surgery (anal sphincter saving or not) and Dukes' tumor stade had an influence on the performance of ART. Thirty-one percent Dukes B tumors and 42.1 percent of Dukes C tumors were irradiated. The practice of ART for these tumors increased significantly from 1978 (18.5 percent) to 1986 (60 percent) (P less than 10(-4)). However, the practice and the distribution of centers performing ART were heterogenous within the department of Calvados. This heterogeneity was neither due to the environment (urban/rural) of the patient nor to the distance between the place of residence and the radiation therapy center. Such an heterogeneity could be explained only by the lack of consensus concerning the practice of ART. Such a consensus could be found considering the results of the latest controlled clinical trials, but definitive conclusions are needed about the effectiveness of ART on the improvement of survival.