Eighty-two patients with adenoid cystic carcinoma treated by a radical course of radiotherapy are reviewed. In 44 cases the tumour arose in the major salivary glands and, of these, 77% had an incomplete surgical excision and 23% had only a tumour biopsy before radiotherapy. Thirty-eight tumours arose in the minor salivary glands and, of these, 18% had an incomplete surgical excision and 82% a biopsy only before treatment. Primary tumour control was achieved in 67% of patients at 5 years. The local control was significantly better in patients who had an incomplete surgical excision: 86% compared with 37% at 5 years. The local control of tumours arising in the major salivary glands is significantly better than that of tumours arising in the minor glands, but this difference is explained by more patients with major gland tumours having had incomplete surgery. For patients treated after only a biopsy, local tumour control was achieved in 37%, demonstrating the radioresponsiveness of this type of carcinoma. No difference in survival was demonstrated in patients with major or minor gland tumours. Despite local tumour control, 43% of patients with major gland tumours died from metastatic disease. The commonest cause of death of patients with minor gland tumours was local failure.