The rationale was to develop recommendations on the use of 18 F-FDG PET in breast, colorectal, esophageal, head and neck, lung, pancreatic, and thyroid cancer; lymphoma, melanoma, and sarcoma; and unknown primary tumor. Outcomes of interest included the use of 18 F-FDG PET for diagnosing, staging, and detecting the recurrence or progression of cancer. Methods: A search was performed to identify all published randomized controlled trials and systematic reviews in the literature. An additional search was performed to identify relevant unpublished systematic reviews. These publications comprised both retrospective and prospective studies of varied methodologic quality. The anticipated consequences of false-positive and false-negative tests when evaluating clinical usefulness, and the impact of 18 F-FDG PET on the management of cancer patients, were also reviewed. Results and Conclusion: 18 F-FDG PET should be used as an imaging tool additional to conventional radiologic methods such as CT or MRI; any positive finding that could lead to a clinically significant change in patient management should be confirmed by subsequent histopathologic examination because of the risk of false-positive results. 18 F-FDG PET should be used in the appropriate clinical setting for the diagnosis of head and neck, lung, or pancreatic cancer and for unknown primary tumor. PET is also indicated for staging of breast, colon, esophageal, head and neck, and lung cancer and of lymphoma and melanoma. In addition, 18 F-FDG PET should be used to detect recurrence of breast, colorectal, head and neck, or thyroid cancer and of lymphoma. PET is an imaging technique that provides unique information about the molecular and metabolic changes associated with disease. The technology has existed for more than 30 years but has been used clinically for only the last 10-15 years. In this period, dramatic improvements in technology, the routine availability of medical cyclotrons (to produce the necessary short-lived positron emitters), and favorable reimbursement decisions in the late 1990s have led to a tremendous increase in the use of this technology. The major area of clinical application is currently in oncology, with some application in cardiology and neurology.PET requires the use of molecules (radiopharmaceuticals) that are labeled with radioactive nuclides. The amounts of radiolabeled material administered are extremely small (10 26 -10 29 g) and have essentially no pharmacologic effect. In this regard, PET has the unique ability to assess molecular alterations associated with disease without perturbing or altering the fundamental underlying molecular and biochemical processes. Although the number of molecular probes that can be radiolabeled with positron emitters is extremely large, and clinical investigational uses number in the thousands, clinical practice has been limited principally to the use of a glucose analog labeled with the positron emitter 18 F-FDG. 18 F-FDG was first synthesized in 1978 (1) and has become the most commonly used radioph...