PET-CT is an acronym for Positron Emission Tomography-Computed Tomography, which combines two machines, PET and CT. The PET provides functional information, including tumour cells, whereas CT provides corresponding anatomical images. Many abnormalities start to appear with the changes in the function of the organ or the body and slowly reflect in the structure. Since PET-CT can image both, it can diagnose the disease early and provide excellent cross-sectional images. Various radio-pharmaceuticals have been discovered to be used in PET-CT machines for different needs of the patients. The most commonly used radiotracers are 18F-FDG, 68Ga-PSMA, 68Ga-DOTA, 18F-DOPA, 18F-PSMA, 18F-Choline, 68Ga-DOTA-Exendine etc. Depending upon the diseased condition, the referring doctors choose appropriate tests for the patients. PET-CT has great use in Oncology, Cardiology, Neurology, and Psychiatry and provides diagnostic information about possible disease origins and their spread in the visualised body. The patients undergo PET-CT for staging, restaging (therapy response assessment), early detection of recurrence of the treated disease, and routine follow-up post-treatment.