Autoimmune pancreatitis (AIP) is responsive to steroid therapy, but some AIP patients improve spontaneously, or only improve after biliary drainage. Pancreatic enlargement and irregular narrowing of the main pancreatic duct usually improves in almost all patients, but marked atrophy of the pancreas develops in some patients. Biliary stenosis improves to various degrees, and a biliary drainage tube can be withdrawn. Other extrapancreatic lesions, including swelling of the salivary or lacrimal glands, lymphadenopathy, and retroperitoneal fibrosis also improve with steroid therapy. Pancreatic endocrine and exocrine function is frequently impaired in AIP patients, and steroid therapy is occasionally effective for these dysfunction. Deterioration of pancreatic exocrine function is rarely detected after steroid therapy. In the literature, the recurrence rate of AIP was reported to be about 17% (range 6% to 26%). AIP patients who relapse during maintenance steroid therapy or after stopping steroid medication should be re-treated with a high-dose steroid. Although AIP is rarely associated with pancreatic stones, stones are formed in some relapsing AIP patients. The long-term prognosis for AIP is unknown. As the pancreatic exocrine and endocrine functions as well as the morphological findings are reversible after steroid therapy, the prognosis for AIP seems better than that of chronic pancreatitis, which is usually followed by exocrine and endocrine pancreatic insufficiency with disease progression. Although carcinogenesis of AIP is unknown, some AIP patients developed a malignancy during follow-up. Since AIP occurs predominantly in the elderly, clinicians should pay attention to any complicating diseases in follow-up of AIP patients. Further studies are necessary to clarify the pathogenesis as well as the long-term prognosis of AIP.