It is generally accepted by surgeons that failure to eradicate malignant disease at the primary site has an adverse effect on survival. The present study investigates 352 patients with squamous carcinoma of the head and neck treated by primary radical radiotherapy and who subsequently underwent surgical ablation for a recurrent carcinoma. A total of 303 (86%) patients had a negative resection margin and 49 (14%) had a positive resection margin. Oral carcinoma was 1.7 times more likely to be associated with a positive margin than other tumours (P = 0.0292). Actuarial calculations demonstrated that 47% of patients with negative margins and 66% of patients with positive margins developed a primary site recurrence (P = 0.0286). Neck node recurrence occurred in 10% of those patients with negative margins and 12% of patients with positive margins. Patients with positive margins had a significantly poorer survival than those with negative margins (P = 0.022). Multivariate analysis failed to confirm any independent adverse effect from a positive margin. The 5 year tumour-specific survival of patients with a positive margin was poorer by 12% than for those patients with a negative margin. The pattern of failure differed between the two groups, with patients having positive margins tending to die of local recurrence.