To define a parameter that quantifies balance control during gait and better identifies elderly people who are at a higher risk of falling.Controlled study.University research laboratory.Twelve elderly patients (mean age, 76.9+/-6y) with complaints of imbalance during walking, or with a history of falls, and 12 matched healthy elderly adults.Not applicable.Temporal-distance gait parameters (gait velocity, stride length, step width); and sagittal and frontal center of mass (COM) and center of pressure (COP) inclination angles.Elderly patients demonstrated a significantly greater medial, but a significantly smaller anterior, inclination angle than their matched controls during both unobstructed and obstructed gait. The medial COM-COP inclination angle was not affected by the gait velocity in the healthy elderly. When the 2 groups were compared at a similar gait velocity ( approximately 1m/s), the elderly patients still had a significantly greater medial COM-COP inclination angle than did the controls.Instantaneous COM-COP inclination angles during walking provide information about the ability to control COM position in relation to the corresponding COP. The medial COM-COP inclination angle may be a sensitive measure of gait stability in the elderly.