A significant bone-mass reduction occurs on the hemiplegic side of stroke patients because of disuse and vitamin D deficiency. This may explain why hip fractures in poststroke patients occur almost exclusively on the hemiplegic side. To further evaluate this osteopenia, bone mineral density (BMD) in both second metacarpals was assessed in 61 patients and 28 control subjects. Serum concentrations of intact parathyroid hormone (PTH), osteocalcin (OC), tartrate-resistant acid phosphatase (TRAP), 25-hydroxyvitamin D (25-OHD), and calcium also were determined. The patients' BMD values were higher on the hemiplegic side than on the nonhemiplegic side. BMD on the hemiplegic side correlated positively with serum concentrations of PTH, OC and TRAP, which exceeded those in control subjects. Serum 25-OHD was low in patients, correlating negatively with BMD on the hemiplegic side. Serum PTH correlate positively with the levels of OC and TRAP and negatively with 25-OHD concentrations. The results indicate that skeletal remodeling is accelerated in patients with hemiplegia, with resorption predominating. We concluded that vitamin D deficiency and compensatory secondary hyperparathyroidism stimulating skeletal turnover is an important cause of osteopenia in the hemiplegic limbs of stroke patients. This osteopenia might be corrected by administration of etidronate to inhibit osteoclastic bone resorption together with a vitamin D supplement.