We herein report the case of a 64-year-old male patient with hypopituitarism associated with autoimmune pancreatitis (AIP). The patient was previously diagnosed with AIP based on the presence of a swollen pancreas, elevated serum immunoglobulin G4, and narrowing of the pancreatic duct by imaging. Magnetic resonance imaging revealed a pituitary stem tumor, and loading test showed a decrease in the function of the anterior lobe suggesting severe failure of growth hormone secretion. Treatment with steroids was effective in reducing the pituitary lesion and improving the function of the anterior lobe. The present case illustrates the importance of pituitary function evaluation before steroid treatment in patients with AIP.