Pure follicular carcinoma of the thyroid gland has become a relatively uncommon type of primary thyroid neoplasm in the United States. During a 20-year period (1962 to 1982) 37 cases of pure follicular carcinoma were treated at the University of Michigan Medical Center. Cases of the follicular variant of papillary carcinoma and Hürthle cell carcinoma were excluded. There were 26 women and 11 men in the series. The mean ages were 46.9 +/- 17.5 and 45.3 +/- 11.5 years, respectively. The overall, mean age was 46.4 +/- 15.9 years. Surgical treatment included total thyroidectomy in 83.8% of the cases. Seventy-six percent of the patients were treated after operation with 131I irradiation. The mean total dose was 230.5 mCi. Three patients (8.1%) had regional lymph node involvement. Six patients (16.2%) had distant metastases to bone and/or lung at the time of diagnosis. Seven patients (18.9%) died after a mean survival of 7.7 years. Six patients (16.2%) died of their disease. Twenty-nine patients (78.4%) are alive and disease free after a mean follow-up interval of 11.8 years. Pure follicular carcinoma is decreasing in incidence and usually occurs at an older age than do other forms of differentiated thyroid cancers. It is frequently more aggressive than papillary carcinoma although lymph node metastases are less common. Total thyroidectomy and 131I therapy are the recommended treatments since metastases to bone and/or lung are the usual locations of distant spread. Bone metastases are rarely if ever cured. However, excellent long-term palliation may be achieved.