Thirty-eight women of postmenopausal age, suffering from fractures of the femoral neck or vertebral bodies were studied in relation to differences in bone metabolism. The blood and urinary changes concerned in mineral and bone metabolism were recorded within 10 days of trauma, and in some femoral neck fractures, a histological study of the femoral heads removed in the course of prosthetic substitution was carried out. The patients with femoral neck fractures were older than those with vertebral fractures and had metabolic and histological findings suggestive of osteomalacia. A particularly significant difference between the two groups was the plasma level of 25 hydroxycholecalciferol, which was lower in femoral neck fractures, and the urinary excretion of calcium, which was also more reduced in femoral neck fractures. A deficit of vitamin D hepatic metabolite thus appears to be a risk factor for femoral neck fractures in old patients.