This study was performed to evaluate local tumour control and toxicity of chemoradiotherapy given to patients with primary or recurrent carcinoma of the anal canal. A total of 117 patients were admitted to the Norwegian Radium Hospital during the period of 1983-1989, of which 106 received a combination of radiotherapy (50 Gy to the pelvis) and chemotherapy (mitomycin C + 5-fluorouracil). Sixty-five percent of the patients with primary carcinomas presented with advanced tumours (T3 or T4). Good local tumor control was obtained as only 25% of the patients with advanced tumours (T3 and T4) and 7% of those with smaller tumours (T1 and T2) had a local relapse after treatment. Recurrent tumours following primary surgery did not respond as well; 50% of these patients still had carcinoma 1 month following therapy. All patients experienced acute toxicity (dermatitis/mucositis, diarrhoea and general fatigue), and 50% needed as split course. There was, however, no therapy-related mortality. Survival data seem promising, but further follow-up is necessary to make conclusions. Eight percent of the patients had serious anal insufficiency after treatment. We conclude that the present regimen provides good local tumour control and well-preserved anal function, but has considerable acute toxicity.