This is a retrospective analysis of 117 patients with carcinoma of the oral tongue treated by definitive radiotherapy during 1979-1990. Sixty-seven per cent of patients presented with T1-2 disease. Their cumulative incidence of local failure was 10% (5/50) for those suitable for treatment with implant alone, 81% (13/16) for those treated with external irradiation alone and 67% (8/12) after combined treatment. These differences could largely be explained by selection factors as smaller and less bulky tumours generally were selected for implant treatment. Among the patients who achieved local control, there was no incidence of regional relapse (0/9) for those with elective neck irradiation, but 33% (15/46) for those without. This incidence correlated with size of primary tumour. Radiotherapy achieved effective local control in 13% (5/39) of T3-4 tumours, and regional control in 43% (12/28) of N1-3 cases. Only 32% (24/76) of patients with local and/or regional recurrence were successfully salvaged. Ways of improving the treatment are discussed.