Thyroid nodules are the commonest disorder presenting to the endocrine surgeon. Most of the lesions are benign, but the principal problem facing the clinician is that of identifying the malignant nodule requiring surgery. Current diagnostic methods are reviewed, and the role of intraoperative frozen section in particular is examined in a series of 155 patients undergoing thyroidectomy for solitary thyroid nodule. It is concluded that when the fine-needle aspiration cytology (FNA) result is malignant intraoperative frozen section is unnecessary and contributes little to the management. Frozen section, however, is considered to be of value when the FNA result is reported as benign, suspicious, or inadequate. It permits identification of many malignant lesions that would otherwise require a second operation to complete a total thyroidectomy. Details of the indications for surgery and the operative strategy are discussed.