The treatment of squamous cell carcinoma of the anal canal remains controversial, and recent reports have recommended combined chemotherapy and radiotherapy rather than radiotherapy alone as primary treatment. In order to define the role for more aggressive local therapy we have performed a retrospective analysis on patients with squamous cell carcinoma of the anal canal treated at the Royal Marsden Hospital between 1958 and 1986. Among 42 patients who received radical radiotherapy (RRT) the overall 5-year caused specific survival (CSS) was 52%. Tumour stage and node involvement were the most important prognostic factors. The 5 year CSS were T1 100%, T2 59%, T3 40% and T4 0% (P less than 0.05). The 5-year CSS for node-negative patients was 64% compared to 23% for node-positive patients (P less than 0.095). A minimum tumour dose of 60 Gy in 30 fractions over 6 weeks was essential to achieve local control and was associated with minimal late morbidity and with the retention of anal continence in all patients locally controlled.