PET/CT is a new imaging technology that has already found a number of clinical applications in oncologic imaging. Widespread introduction into clinical practice started approximately 2.5 years ago. Consequently, the available data are largely preliminary. Nevertheless, it can already be stated that the synthesis of structural and metabolic information improves the accuracy of primary staging and the detection of recurrent disease and has the realistic potential to change patient management in 10 to 20% of cases. PET/CT fusion images can directly guide biopsies or surgical interventions. This article summarizes preliminary data of PET/CT studies and highlights potential clinical applications for PET/CT, with particular emphasis on lymphoma, melanoma and gastrointestinal tumors.