Because it may be difficult to evaluate gastrointestinal diseases in children with insulin-dependent diabetes mellitus (IDDM), this report highlights several clinical features unique to diabetes and emphasizes the relationship between gastrointestinal pathology and glycemic control. Two children with IDDM are described whose hyperglycemia, ketosis, and abdominal pain were the presenting features of H. pylori-positive duodenal ulcer disease and acute appendicitis, respectively. A third nondiabetic child developed persistent postprandial hyperglycemia as the initial manifestation of dumping syndrome. These patients illustrate the relationship between glycemic control and gastrointestinal pathology in children with diabetes and the effects of gastrointestinal dysfunction on glucose regulation in nondiabetic children. In children with IDDM, gastrointestinal pathology can be confused with ketoacidosis and complicate diabetes control and management. Early recognition and treatment of the underlying gastrointestinal disease often improves glycemic control. Furthermore, severe gastrointestinal dysfunction in nondiabetic children may deleteriously influence glycemic regulation and may be confused with childhood diabetes.