In 175 patients presenting with thyroid nodules, the diagnostic value in management offine needle aspiration and cytology (FNAC), pertechnetate ( 99mTc) scanning and ultrasound imaging was examined. In 82 patients, the diagnosis was confirmed at operation; in the remaining 93, there was a follow-up period of at least 2 years. Thyroid cancer was found in 13 patients. For FNAC the sensitivity, specificity and positive predictive value for thyroid cancer were 92%, 85% and 41% respectively compared with 82%, 34% and 11% for 99mTc pertechnetate scanning, 75%, 61%, 19% for ultrasound and 73%, 58% and 19% for combined pertechnetate and ultrasound scanning. In 14% of patients, the aspirates were inadequate for cytology at the first examination. FNAC is therefore the preferable initial investigation and usually gives results adequate for a decision on surgical or medical management. With medical management and follow-up, ultrasound is of value in defining the nodule and the appearance of the rest of the gland.