Two cases of adult T-cell leukemia associated with acute pancreatitis due to hypercalcemia. We report two cases of adult T-cell leukemia associated with acute pancreatitis and hypercalcemia. After sudden onset of epigastralgia, acute pancreatitis and hypercalcemia were found in both patients. There were no diseases that could explain the acute pancreatitis except for hypercalcemia probably due to adult T-cell leukemia. Thus we considered that hypercalcemia due to adult T-cell leukemia had led to acute pancreatitis. This is the first report of such a complication in adult T-cell leukemia. 