Solitary thyroid nodule: a prospective evaluation of nuclear scanning and ultrasonography. The aim of this study was to assess prospectively the value of thyroid nuclear scans and ultrasound examination in the preoperative investigation of patients with a solitary thyroid nodule. Total thyroid lobectomy for a solitary thyroid nodule was performed in 68 cases. Each patient had a thyroid isotope scan (except two women who were pregnant) and thyroid ultrasound examination. There were 10 (15 per cent) malignant nodules, 11 (16 per cent) benign neoplastic nodules and 47 (69 per cent) benign non-neoplastic nodules. All of the patients with malignant nodules who were scanned had a solitary cold nodule on thyroid scan, as did 40 (69 per cent) of those with benign solitary nodules. Ultrasound examination of the thyroid suggested correctly that one of 16 (6 per cent) cystic lesions, four of 16 (25 per cent) complex solid-cystic lesions and three of 18 (17 per cent) of solid lesions were malignant. One lesion reported as multinodular on ultrasonography and one reported as normal also turned out to be malignant. Thyroid isotope scans and ultrasound do not accurately differentiate between benign and malignant conditions and their routine use in the investigation of a solitary thyroid nodule should be abandoned. 