Fever of unknown origin (FUO) is a major diagnostic challenge worldwide. Causes of FUO range from infectious diseases to malignancies and sometimes inflammatory disorders. There have been major advances made in various diagnostic fields which help in diagnosis of FUO. FDG-PET (Fluorodeoxyglucose Positron emission tomography) scans are being found helpful in diagnosing many rare causes of FUO. Here we present a rare case of FUO in which we could arrive at the diagnosis after the PET scan which showed Aorto-arteritis. Hence we concluded that PET scans may be used in diagnosing non-infectious and inflammatory causes of FUO where the preliminary investigations could not help in the diagnosis.