The clinical notes of all new patients with T1 squamous cell carcinoma of the glottis seen in one head and neck cancer unit between 1989 and 1996 were reviewed. Fifty-three patients were treated with radical radiotherapy and of these 42 (79.2 per cent) had no loco-regional recurrence, after a median follow-up of seven years. Eleven (20.8 per cent) developed local recurrence and were treated with salvage surgery. Fourteen of the 53 (26.4 per cent) tumours involved the anterior commissure and eight of these 14 (57.1 per cent) developed recurrence, whereas only three of the 19 (15.8 per cent) tumours arising from the anterior half of the fold but not involving the anterior commissure had recurrence. None of the remaining tumours recurred. This difference is statistically significant (p<0.001). Anterior commissure involvement is a predictor of poor response to radiotherapy. This may be the result of understaging as none of the cases had computed tomography (CT) scans performed. Technical radiotherapy factors may also be important, although in all cases of anterior commissure involvement steps were taken to ensure adequate radiation dose to this region.