We have implemented a fine needle biopsy program, evaluating 426 satisfactory biopsies in 436 patients with thyroid nodules. Benign disease was diagnosed in 345 patients (232 with benign nodular goiter, 98 with lymphocytic thyroiditis, three with granulomatous thyroiditis, and 12 with cysts). Neoplasm was diagnosed in 81 patients (61 with follicular neoplasm, 12 with papillary carcinoma, three with medullary carcinoma, three with anaplastic carcinoma, one with metastatic carcinoma, and one with lymphoma). Of the 43 patients who later proved to have cancer, 24 had follicular carcinoma, 12 papillary carcinoma, one medullary carcinoma, three anaplastic carcinoma, one metastatic carcinoma, and two lymphoma. (Eight patients refused surgery or were operated upon elsewhere and lost to follow-up.) Cancer was found in 54% of patients sent to surgery. Follicular carcinoma cannot presently be separated from follicular adenoma by needle biopsy, and surgery will continue to be required in these patients (14%); however, thyroid biopsy greatly decreased the need for surgery in other patients. Erroneous diagnoses, mainly due to inexperience, decreased after the first year. A multidisciplinary approach involving the thyroidologist and cytopathologist is important, as is the close clinical follow-up of patients with nodules thought to be benign. The safety of needle biopsy, its low cost, and the accuracy of the procedure when compared to other clinical tests for thyroid nodules make it well worth the effort to make this test more widely available.