Pathologic and point count-morphometric studies of ribs, vertebrae, and iliac crests of 7 patients with Von Gierke's glycogenesis type Ia aged 5 months to 30 years were performed. The bone lesion is a pure osteoporosis (reduction in mass of bone matrix) with no evidences of significant physeal cartilage abnormality or of osteitis fibrosa or osteomalacia (reduced mineralization of bone matrix). The osteoporosis was already marked in the youngest patient studied (5 months). The discrepancy between normal and glycogen storage disease (GSD) bones increased progressively with age for ribs and was less severe for vertebrae. Available biochemical data give no indication of primary disturbance of calcium or phosphate metabolism, of parathyroid activity, or of vitamin D metabolism. Clinical data suggest that the osteoporosis of Von Gierke's disease is due to hypoglycemia or a metabolic sequela thereof, such as insulinopenia, but pathologic study of patients treated by newer techniques of maintaining euglycemia in GSD is needed.