Cerebral infarction is one of the serious neurological complications of diabetic ketoacidosis (DKA). Especially in patients who are genetically prone to thrombosis, cerebral infarction may develop due to inflammation, dehydration, and hyperviscocity secondary to DKA. A 6-year-old child with DKA is diagnosed with cerebral infarction after respiratory insufficiency, convulsion, and altered level of consciousness. Femoral and external iliac venous thrombosis also developed in a few hours after central femoral catheter had been inserted. Heterozygous type of factor V Leiden and PAI-1 4G/5G mutation were detected. In patients with DKA, cerebral infarction may be suspected other than cerebral edema when altered level of consciousness, convulsion, and respiratory insufficiency develop and once cerebral infarction occurs the patients should also be evaluated for factor V Leiden and PAI-1 4G/5G mutation analysis in addition to the other prothrombotic risk factors.