In 175 patients presenting with thyroid nodules, the diagnostic value in management of fine 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.