Immunoglobulin G4 (IgG4)-related disease is known to mimic multiple malignancies and always poses a diagnostic challenge. We report a case of a 20-year-old young man, who presented with unexplained recurrent episodes of fever and pain abdomen. F-FDG PET/CT revealed intense focal FDG avidity in the prostate. On further workup, he had an elevated serum IgG4 level, and a clinical diagnosis of immunoglobulin G4-related disease was kept. A follow-up FDG PET/CT after glucocorticoid therapy revealed resolution of FDG avidity in the prostate with fall in serum IgG4 levels, hence confirming a diagnosis of atypical immunoglobulin G4-related disease involving isolated prostate gland.