A 15-year-old girl was referred to the hospital because of abdominal pain and bloody stools.The patient had been in excellent health until 26 weeks earlier, when she began to have mild periumbilical pain, usually after the evening meal, without radiation to the back. She passed small amounts of blood with several stools and sometimes noted blood dripping into the toilet bowl. She continued to have periumbilical pain. The results of laboratory studies performed at that time and on four subsequent occasions before admission are shown in Tables 1 and 2. A stool culture was negative; Clostridium difficile toxin was not detected, and no ova or parasites were found.The results of an ultrasonographic examination of the abdomen and an upper gastrointestinal series with a small-bowel follow-through study, performed 25 weeks before admission, were normal. A sweat chloride test was negative. Treatment with a low-fat diet and pancreatic-enzyme replacement was begun 20 weeks before admission.Fifteen weeks before admission, the abdominal pain had mostly disappeared, but slight rectal bleeding continued intermittently. A magnetic resonance imaging (MRI) examination of the pancreas, performed after the administration of gadolinium, showed enlargement and heterogeneous enhancement of its head and slight dilatation of the pancreatic duct (3 to 4 mm), with slight beading within the body of the pancreas -findings consistent with the presence of chronic pancreatitis.Thirteen weeks before admission, the abdominal pain had resolved, and the girl no longer had hematochezia. Nine weeks before admission, she had a two-week bout of abdominal pain and diarrhea with-*To convert the value for iron to micromoles per liter, multiply by 0.1791. To convert the value for cholesterol to millimoles per liter, multiply by 0.02586. To convert the value for triglycerides to millimoles per liter, multiply by 0.01129. †The normal range is 37 to 170 mg per deciliter. ‡The normal range is 30 to 100 U per liter. §The normal range is 25 to 100 U per liter. ¶The normal range is 10 to 30 U per liter.