OBJECTIVES. Positron Emission Tomography with 18F-fluorodeoxyglucose (FDG-PET) is a new nuclear imaging technique that can detect recurrent or metastatic thyroid carcinomas. We conducted a systematic review to determine the diagnostic accuracy of FDG-PET in patients with papillary and follicular thyroid carcinoma. METHODS. Two unblinded reviewers independently selected, extracted and assessed data from relevant literature. Included studies were prospective or retrospective with 10 human subjects or more that evaluated the accuracy of FDG-PET in follicular and papillary thyroid cancer. Reviews, case reports, editorials, letters, and comments were excluded. The methodological quality of the included studies was assessed by the criteria for diagnostic tests recommended by the Cochrane Methods Group on Screening and Diagnostic Tests. A qualitative analyse was conducted to assess the value of FDG-PET in thyroid carcinoma. The rating system consisted of four levels of scientific evidence (1=best; 4=worst). RESULTS. Two of the fourteen included studies were considered of level 3 evidence. The other twelve studies provided level 4 evidence. Most prevalent methodological flaws regarded validity of reference tests and blinding of test interpretation. The overall conclusion in these studies was that FDG-PET appeared beneficial in patients with elevated thyroglobulin levels and negative 131I WBS. CONCLUSIONS. In conclusion, although FDG-PET may solve clinical problems in selected patients suspected of recurrent thyroid cancer, the present evidence does not allow for implementation of a routine diagnostic algorithm. Future studies should be designed to avoid the limitations presented in this review.