Since the inception of positron emission tomography many decades ago, this imaging modality has grown appreciably as one of the most valued imageology in both health and disease. Once upon a time PET had mere 20 detector elements, 2cm axial field of view and spatial resolution of approximately 25mm.Last couple of years witnessed its metamorphosis into 25000 detectors, 20cm field of view and 5mm spatial resolution. As a result, clinical applications of PEt also grew tremendously. The current articles reviews the early days of PET, radioisotopes, radiopharmaceuticals used, principal basis of PET and clinical applications.