PURPOSE: To assess the acute toxicity and hence feasibility of postoperative hyperfractionated accelerated radiotherapy in rectal cancer. METHODS AND MATERIALS: Twenty patients were submitted to accelerated hyperfractionated radiotherapy after resection of rectal cancer. A total dose of 48 Gy was given in 3 weeks. Two fractions of 1.6 Gy were used with a mean interfraction interval of at least 6 hours. The pelvic volume was treated by a four-field box technique using a linear accelerator (6-18 MV). Acute toxicity was assessed once per week. Small bowel and skin toxicity were scored according to the criteria of the World Health Organization. Bladder toxicity was scored according to the criteria of the Radiation Therapy Oncology Group. RESULTS: All the patients underwent the treatment as planned except one. No patient presented grade 3 or 4 bladder toxicity. There was only one patient who complained from grade 3 skin toxicity at the end of the treatment. Fourteen patients had some degree of intestinal toxicity. This was the most frequently occurring acute side-effect. Only two out of the fourteen patients had intestinal toxicity exceeding grade 2. CONCLUSION: Hyperfractionated accelerated radiotherapy on a pelvic volume is feasible as far as acute toxicity is concerned.