A 7-year-old boy with Cori type I glycogenosis (glucose-6-phosphatase deficiency) who manifested extreme hyperlipemia and eruptive skin xanthomas was given medium chain triglycerides as the sole source of fat in his diet. Serum total lipids decreased significantly within 14 days, and skin xanthomas cleared completely four months after the diet containing medium chain triglycerides was instituted. The findings suggest that careful regulation of the diet, particularly fat intake, is indicated in the management of eruptive xanthomas and other lipid abnormalities in this disorder.