In order to analyze balance control, we developed a new inclinometry-based method to provide direct information about body sway in the side-to-side and forward-backward directions. We tested the clinical utility of this method for analyzing balance in Parkinson's disease (PD), and studied the clinical correlates of the balance measures in PD. Postural sway was measured during quiet stance with eyes open and eyes closed in 28 PD patients and in 32 age- and sex-matched control subjects. Postural sway was modeled using side-to-side and forward-backward directional sway movements, sway velocity, and sway area. The amount of postural sway in the PD patients was greater than in the control subjects, the higher level being most marked in patients with severe or long-duration PD. All the side-to-side directional sway parameters were abnormal in the PD patients compared with the control subjects (P < 0.05), whereas the forward-backward directional parameters did not differentiate the two groups. The most sensitive measures of sway were path length, velocity, and area. The duration and severity of PD seem to be particularly associated with the amount of side-to-side directional postural sway. This new inclinometric method appears to be useful in quantifying postural sway and evaluating balance impairment in PD.