Nuclear Medicine offers several possibilities for the imaging of inflammatory bowel diseases (IBD). Most data available in the literature concern the use of radiolabelled autologous white blood cells (WBC). With this method it is possible to evaluate with a single scan the whole body and, therefore, depict the extent of pathological gut wall infiltration by leucocytes: a sign of disease activity. The method of WBC has been criticised for its long preparation time and lack of anatomical accuracy. However, there are now available several kits for easy labelling of WBC with 99mTc and the possibility to use hybrid SPECT/CT cameras that improve accuracy and anatomical localisation of lesions. These kits can also use 18 F and 64Cu for WBC labelling, two positron-emitting isotopes, that allow PET/CT imaging with further improvement of image detail and possibility to quantify uptake in lesions for early therapy follow-up. But the availability of new SPECT and PET radiopharmaceutical for molecular imaging and for in vivo histological characterisation of lesions has recently opened a new indication for IBD that is therapy decision making. We can quantify the presence of activated T-cells or lymphokines (such as TNFa) in gut wall lesions, thus providing the clinician with important information for starting the appropriate treatment and to early assess (within weeks) the efficacy of the treatment. Since MRI and Nuclear Medicine are complementary for the study of IBD, we aim at clarifying what is the role of both methods and how to integrate them in the diagnostic flow-chart of patients. The future will probably be a single scan with PET/MRI hybrid cameras, recently available. Learning Objectives: 1. To highlight available imaging methods, imaging techniques and diagnostic algorithms for the evaluation of inflammatory bowel lesions. 2. To learn more about the specificity of nuclear medicine techniques and their clinical role. 3. To understand the role of nuclear medicine imaging in the evaluation of disease activity and extent, therapy decision making and early therapy follow-up.