We studied the records of patients with Hürthle cell neoplasms seen at the University of California at San Francisco, from 1943 to 1982, because of controversy concerning the malignant potential of these tumors. Of our 84 patients, 71 had Hürthle cell adenomas (HCAs), nine had Hürthle cell change in chronic thyroiditis, and four had Hürthle cell carcinomas. Coexisting papillary thyroid carcinoma occurred in three patients with HCA. Twelve patients with HCAs had multiple lesions, five of which were bilateral. Patients with HCA were followed up for 675 patient-years, 45 for four years or more (maximum duration, 36 years). There were no recurrences or deaths among the patients with benign Hürthle cell tumors. Thus, patients with HCA had a benign course, and histologic examination results accurately reflected malignant potential.