The use of PET (positron emission tomography) has become the standard quality of care for optimal management of patients with cancer. The availability of the hybrid PET/CT (positron emission tomography/computed tomography) scanner has further improved the utility of PET scanning and provides additional benefits both to patients and to the health system. This publication addresses the important issue of appropriateness of the application of PET/CT procedures in different clinical scenarios for many cancers. It is a resource for specialists in nuclear medicine and oncology, and aims to make reliable information widely available to those Member States where PET programmes are still in their planning phase or where the use of PET scanning is limited.