Use of PET is widespread and increasing in the United States, mainly for oncologic applications. In November 2006, the National Comprehensive Cancer Network (NCCN) gathered a panel of experts to review the literature and develop clinical recommendations for using PET scans in lymphoma and non-small cell lung, breast, and colorectal cancers. However, because its use is not restricted to these diseases, and evidence is accumulating for its application in other types of cancers, NCCN convened a second meeting in December 2008 to expand on the initial report. A multidisciplinary panel met to discuss the current data on PET application for various tumor types, including genitourinary, gynecologic, pancreatic, hepatobiliary, thyroid, brain, small cell lung, gastric, and esophageal cancers, and sarcoma and myeloma. This report summarizes the proceedings of this meeting, including discussions of the background of PET, the role of PET in oncology, principles of PET use, emerging applications, and possible future developments.