From 1979 to 1988 63 patients with cancer of the colon received postoperative adjuvant radiotherapy. The mean age was 62 years and the median follow-up period was 71 months. Pathologic staging showed a B1-tumour in nine cases, B2 in 25, C1 in three and a C2-tumour in 26 cases according to the Astler and Coller modification of the Duke's classification. 53 patients received doses between 41 and 50 Gy. 47 patients were treated with a 60Co megavoltage unit and 16 cases with 8 MV photons. The overall five years survival rate is 65%. There was no significant difference between the survival rates for all stages. Only four patients with primary positive lymph nodes experienced a local relapse. 16 developed metastatic disease. In twelve cases (19%) liver metastases appeared: four patients (6%) developed intraperitoneal metastases, one patient had a metastasis in the abdominal wall and another showed pulmonary carcinosis. Acute and transient side effects were seen in 35% of our patients. Three patients underwent a second operation for radiation induced bowel stenosis. Compared with the results of surgery adjuvant radiotherapy yields improved five-year survival data in patients with C2 and G4 tumours.