The characteristic of nuclear medicine is that it gives images of organs, structures and physiological or pathological processes, detecting the distribution of several radio-pharmaceuticals according to their uptake and metabolism. Its imaging can provide morphological information while at the same time containing data on cellular activity and functions. Such molecular imaging fulfils the modern orientations of oncology, where there is a need to define the presence of a malignancy in the earliest and most effective way, to characterise the neoplasm in terms of biological characteristics (e. g., proliferation, aggressiveness, differentiation, receptor status) and to obtain fundamental issues in patient management such as evaluation of disease extent, monitoring of therapies and study of treatment-induced side effects. The aim of this position paper is to discuss the main indications of nuclear medicine in diagnostic oncology reporting the most recent developments in nuclear medicine, and an extensive list of the major indications for nuclear medicine procedures. The techniques have been labelled as when considered essential in the diagnostic process, when they can give useful additional or information in combination with other instrumental diagnostic approaches, and alternative when they may be performed instead of other tests. These indications were derived by a general consensus within the Task Group of Oncology of the World Federation of Nuclear Medicine and Biology, and it should be stressed that only the current role of nuclear medicine was considered. The Task Group does not claim to have covered the entire range of nuclear medicine indications; in fact it was agreed to include only the most widely used techniques. The highly specific or very exceptionally used applications, or those still in development or under evaluation in clinical trials were not taken into consideration. The conclusion is that the current relationship between nuclear medicine and oncology can be defined not only as satisfactory but also as extremely promising, as nuclear medicine has the potential to compete with the most advanced radiological techniques of imaging, perhaps not so much in terms of sensitivity but more so in terms of specificity and biological characterisation. Several novel diagnostic procedures are able to solve clinical problems for which traditional radiology has shown clear limitations. Nuclear medicine remains today a dynamic medical specialty because it includes a combination of advances in basic science research, technology, cell biology and medical practice and it cannot be excluded that the new lines of research both towards new radiopharmaceuticals and advanced instrumentation will offer in the future new stimulating opportunities.