A wide variety of adverse effects of methimazole (MMI) have been reported. Here we report a new MMI-induced disorder, acute pancreatitis and parotitis. Three weeks after a woman started MMI treatment for Graves' disease, she developed a high fever, painful parotid swelling and dull pain in the upper abdomen with elevation of the serum levels of salivary and pancreatic enzymes. These abnormalities disappeared soon after the withdrawal of MMI. However, the same abnormalities were rapidly provoked when MMI was reintroduced. Marked increases in the leucocyte count and CRP were also observed during these episodes. The possible mechanisms of MMI-induced pancreatitis/parotitis are discussed.