The cortical bone mineral density (BMD) of the first metatarsus was measured using computed x-ray densitometry in 84 hemiplegic subjects (35 men and 49 postmenopausal women) and 49 healthy age-matched controls (23 men and 26 postmenopausal women), and the determinants of paralysis-induced cortical osteopenia were investigated. In the hemiplegia group, ages were 63.9 +/- 9.8 yr (mean +/- standard deviation) for men and 66.6 +/- 11.0 yr for women. The duration of hemiplegia was 25.3 +/- 19.8 mo for men and 26.0 +/- 26.3 mo for women. The Brunnstrom stage (lower limb) was 4.0 +/- 1.1 for men and 3.8 +/- 1.4 for women. The walking ability, evaluated by walking score, was 3.6 +/- 1.3 (range, 1-5) for men and 3.2 +/- 1.5 (range, 1-5) for women. The time since menopause was 14.8 +/- 10.0 yr. The age and time since menopause were similar in the hemiplegia and control groups. On the paralyzed side, the BMD of men and women in the hemiplegia group was significantly lower than that of the control group on the nondominant side (by 6.1% and 11.6%, respectively). In hemiplegic men, Brunnstrom stage and walking score showed a significant positive correlation to the BMD (r = 0.418 and r = 0.349, respectively). In hemiplegic women, on the other hand, age, duration of hemiplegia, and years since menopause showed a significant negative correlation to the BMD (r = -0.260, r = -0.478, and r = -0.506, respectively), and Brunnstrom stage and walking score showed a significant positive correlation to the BMD (r = 0.526 and r = 0.406, respectively). These findings suggest that the determinant of metatarsal cortical BMD loss on the paralyzed side of the hemiplegic subject might be different according to gender. That is, although the degree of paralysis and walking ability could be a determinant of metatarsal cortical BMD loss on the paralyzed side of hemiplegic men, additional factors such as age, duration of hemiplegia, and years since menopause could play an important role in the determination of metatarsal cortical BMD loss in postmenopausal hemiplegic women.