Between 1975 and 1990, eighteen patients with a histologically proven diagnosis of chordoma were treated at our institution. All patients initially underwent a surgical procedure and were referred for irradiation due to residual disease or postsurgical relapse. The mean dose administered was 50.1 Gy (range, 29.9-64.8 Gy). Eight patients were treated according to a hyperfractionated schedule. The overall actuarial 5-year survival and 5-year progression-free survival were 38% and 17%, respectively. The progression-free interval was longer for patients receiving doses greater than 48 Gy when compared with doses below 40 Gy (actuarial 5-year progression-free survival of 31 +/- 35% vs. 0%, respectively; p = 0.04). We conclude that in the treatment of chordoma, the administration of high radiation doses may increase the disease-free interval. The objective response and dose-response relationships were analyzed in twelve patients for whom sequential CT scans were available.