Only two studies were sufficiently powered to provide potentially reliable estimates of PET sensitivity and specificity for diagnosing metastatic disease in patients with treated differentiated thyroid cancer, elevated thyroglobulin, and negative (131)scintigraphy. However, the poor quality and small size of these studies limit the reliability of the test performance estimates. Smaller studies reported wide ranges of sensitivity and specifity. Insufficient data exist to estimate the test performance of PET for treated medullary thyroid cancer or other rarer forms of thyroid cancer. Limited data suggest that PET may affect management of patients with differentiated cancer and may result in cure of at least on-third of such patients. However, study quality was too poor and follow-up duration was too short (or not reported) to allow a definitive conclusion. Insufficient data exist to estimate the effect of PET on treatment management of patients with medullary or other rarer forms of thyroid cancer. Overall study quality was poor and study sample sizes were small. Future well-designed, clearly reported studies that focus on patients with treated thyroid cancer, elevated biochemical markers of metastasis and negative standard imaging tests are needed to define best performance and effect on clinical management and outcome of PET.