A retrospective analysis of clinical and pathological data was conducted on 706 patients (514 females and 192 males) treated for differentiated thyroid carcinoma at The University of Texas M. D. Anderson Hospital and Tumor Institute at Houston from 1951 to 1975 and followed to 1981. The histological diagnoses were mixed papillary/follicular carcinoma (66.7%), papillary carcinoma (14.6%), follicular carcinoma (15.3%), or Hurthle cell carcinoma (3.4%). Patients diagnosed before the age of 40 yr lived significantly longer than those diagnosed over the age of 40 yr, and females lived longer than males. According to survival analyses and disease-free intervals, the order of increasing aggressiveness of the tumors was papillary, mixed, follicular, and Hurthle cell. Total thyroidectomy was associated with longer disease-free intervals and fewer recurrences. The 136 patients who received ablative 131I after surgery had fewer recurrences than a matched group who did not, but the disease-free interval and survival rate showed no significant difference. Further classification showed that patients with follicular and mixed tumors, and those who underwent total thyroidectomy benefited from 131I. There were 78 deaths attributed to thyroid cancer in the whole group. Approximately two thirds occurred in the first 10 yr after diagnosis. In conclusion, total thyroidectomy is recommended, when feasible, for differentiated thyroid cancer, followed by ablative 131I therapy, at least for follicular and mixed varieties.