Autoimmune pancreatitis (AIP) is most often incidentally detected, with the diagnosis being based on radiological characteristics. A steroid regimen for 6 weeks is the standard line of treatment for AIP. In our case, AIP was incidentally suspected on fluorodeoxyglucose positron emission tomography/computed tomography (PET/CT) performed for staging a malignancy, and a follow-up PET/CT study after steroid treatment, showed complete metabolic and morphological response; thus confirming the imaging diagnosis of AIP.