Previous studies have demonstrated that hip fractures in stroke patients occurred almost exclusively on the hemiplegic side. We examined the bone changes in the second metacarpal of the hemiplegic side in terms of microdensitometric indices in 93 stroke patients with hemiplegia. All six indices indicated a significant decrease in bone mass on the hemiplegic side compared with the contralateral side. Differences in the indices between the hemiplegic and contralateral sides were correlated well with the duration of the illness and Brunstrom's stage for finger, arm, and leg. The same degree of osteopenia occurred in both small capsular and large hemispheric lesions. The same osteopenia was demonstrated in paralyzed and immobilized patients with myopathy. Thus a combination of weakness and immobilization is thought to be responsible for the osteopenia in the hemiplegic metacarpal bone. The osteopenia noted in the second metacarpal in the affected limb may account for the fact that hip fractures in stroke patients occur almost exclusively on the hemiplegic side.