Nine hundred thirty-two patients with papillary and follicular thyroid carcinomas were seen at the Departments of Medicine, Surgery, and Radiology of the University of Essen, Essen, Germany, between 1970 and 1986. In addition to standard treatment by surgery, radioactive iodine and medical thyroid stimulating hormone (TSH) suppression, 346 patients had received conventional external irradiation to the neck (mostly 40-60 Gy) before referral to our institutions, whereas 586 patients had not received radiotherapy. From the follow-up data of these patients, survival rates were calculated separately for tumor Stages T1 (n = 203), T2 (n = 552), and T3/T4 (n = 277) using life-table analysis. Distribution of risk factors (histologic type of tumor, grading of malignancy, presence of distant metastases, age and sex) was similar in all groups with the one exception, that the radiotherapy patients with Stage T3/T4 were older. There was no significant difference in the life expectancy of irradiated and not irradiated patients by Breslow and Mantel-Cox tests. In Stages T1, T2, and T3/T4, 75% of the radiotherapy patients survived for 10.6 +/- 0.32, 11.5 +/- 0.61, and 6.71 +/- 0.85 years, respectively; the figures for the nonirradiated patients were 9.4 +/- 0.17, 10.8 +/- 0.37, and 6.26 +/- 0.51 years, respectively. When survival rates were calculated separately for patients with Stage T3/T4 older and younger than 40 years, there was no obvious effect of radiotherapy in the younger group, whereas in the older patients, improvement of survival by radiation just failed to reach statistical significance (P less than 0.09). In conclusion, this retrospective analysis failed to prove that survival is prolonged in patients with differentiated carcinoma by administration of conventional external radiotherapy after surgery. A benefit to older patients with locally advanced tumors has still to be demonstrated.