A total of 1249 "cold" solitary thyroid nodules were excised at the Brigham and Women's Hospital from 1948 through 1987. Of these nodules, 241 showed malignant conditions: 123 were papillary, 42 were mixed papillary-follicular, and 43 were pure follicular carcinomas. There were also 23 anaplastic, 8 medullary, and 3 Hürthle cell carcinomas. These patients were followed up from 3 to 31 years, with a mean range of 10 years. Fifty-three patients with well-differentiated tumors underwent total thyroidectomies, and 179 underwent subtotal thyroidectomies (excluding anaplastic, medullary, and Hürthle cell tumors). Regional lymph node involvement was commonly found but appeared not to affect survival; tumor size and local spread and extent of thyroid gland involvement did affect survival. A small percentage of well-differentiated thyroid tumors do, in time, undergo anaplastic change that leads to metastasis and death. There was no 30-day mortality rate. The late mortality rate was 2% for papillary and 14% for follicular carcinomas. Papillary tumors are becoming more common. Older aged patients and male patients appear to carry poorer prognoses for survival. The total thyroidectomy procedure has not improved survival over subtotal thyroidectomy and carries a higher complication rate.