Severe partial seizures may be the presenting feature of nonketotic hyperglycemia in older adults, but cases in children are rare. We report three teenagers with well-controlled epilepsy who suddenly developed intractable partial seizures poorly responsive to anticonvulsants. Blood glucose levels were measured only after several days of hospitalization for frequent seizures when mild polyuria and polydipsia were first noted. Glucose levels were high with mild ketosis and acidosis in one patient and no ketosis in two. With institution of insulin, there was prompt cessation of seizures. The patients were diagnosed as having type I insulin-dependent diabetes mellitus and require ongoing insulin treatment. Hyperglycemia should be considered in children with epilepsy who develop intractable seizures.