A static force plate system was used to examine postural sway characteristics in 16 hemiplegic patients and in 34 normal elderly subjects. The effectiveness of postural sway (center of pressure) biofeedback was compared to conventional physical therapy practices in reestablishing stance stability in hemiplegic patients. Postural sway abnormalities in hemiplegic patients included significant mean lateral displacement of sway towards the nonaffected leg and increased total sway area. Postural sway biofeedback was more effective than conventional physical therapy practices in reducing mean lateral displacement of sway. This was associated with increased loading of the affected leg. Posttreatment changes in total sway area were not significantly different between experimental and control groups.