Twenty patients of chronic thyroiditis without neoplasm were operated in our department from September 1986 to August 2000. Of these patients, 15 were suspected the involvement of malignant tumors preoperatively, and 6 were observed class IlI by fine needle aspiration cytology (FNA). Hemithyroidectomy and partial resection were conducted in 17 patients, and subtotal and/or total thyroidectomy were conducted in 3 patients. Two patients underwent total thyroidectomy had dyspnea or swallowing disorder. Class i by FNA is sometimes observed in the patients with chronic thyroiditis, then the carefull interpretation for class III is proposed. Thyroid associated autoimmune antibodies (at least anti thyrogurobulin antibody) is necessary for the diagnosis of chronic thyroiditis. The operation for the chronic thyroiditis without malignancy is proposed to avoid by the accurate diagnosis of chronic thyroiditis.