Positron emission tomography (PET) is an imaging technique using positron (anti-electron) radiopharmaceuticals, in which radiation generated during the annihilation of positrons is recorded. This method is used in oncology, neurology and cardiology. PET is of particular importance to oncology, in both scientific and clinical research, especially in the identification and staging of metastatic disease, as well as in therapy planning and control. The use of PET has contributed to the advancement of research into many neurological problems. Data in the literature indicate that PET is widely used in veterinary medicine. PET allows for detailed evaluation of many oncologic and fungal diseases. In neurology, it has been used in necrotizing meningoencephalitis and epilepsy. There have been a number of experimental studies in cardiology, as well, in patients after radiation therapy.