Two children with acute lymphoblastic leukemia/lymphoma developed recurrent acute pancreatitis during treatment; the etiology was presumed to be secondary to 6-mercaptopurine (6MP). Both had no further attacks after discontinuation of 6MP. Acute pancreatitis secondary to 6MP is extremely rare in acute leukemia/lymphoma although it has been reported in patients with other conditions like inflammatory bowel disease; the reason for this difference is not clearly understood.