Although glycogen storage disease type 0 (GSD0) is included in the differential diagnosis of ketotic hypoglycemia, it usually is not considered in the evaluation of glucosuria or hyperglycemia. We describe two children with GSD0, confirmed by mutation analysis, who had glucosuria and hyperglycemia. Because of the variable presentation of this disorder and previous dependence on liver biopsy to confirm diagnosis, it is likely that GSD0 is underdiagnosed.