A personal series of 3,215 patients with proven squamous cell carcinoma of the mucosal surfaces of the upper aerodigestive tract is presented. Of these patients, 515 suffered a recurrence of their primary tumor after a course of radiotherapy. The time from the end of radiotherapy to diagnosis of a primary recurrence was not related to any known host factors, nor to tumor factors except site. However, it was the most significant predictor of survival, both from initial presentation and from the date of recurrence. The time to recurrence did not relate to the size of the tumor at recurrence, suggesting that large recurrences are multicentric. The time to recurrence also predicted response and survival of 67 patients with end-stage disease treated by chemotherapy. The response and survival were better in tumors with a time to recurrence longer than the median; the increased survival was not significant, but the increased response was.