This study was conducted to evaluate the clinically apparent balance improvements in a patient with Parkinson's disease who had stimulating electrodes surgically implanted to the VIM nucleus of the right thalamus for control of left-upperextremity tremor. Experiments were conducted to determine if balance improved simply because the large-amplitude upper-extremity tremor was reduced or if the neural control of the thalamic stimulation on the contralateral upper-extremity tremor and on the lowerextremity postural muscle activatios for quiet stance, step initiation, and equilibrium responses to surface displacements. The results demonstrated that, beside reducing the amplitude and destabilizing effects of the upper-extremity tremor, the thalamic stimulation was also effective in reducing tremor activity of the trunk and contralateral lowerextremity muscles. In addition, the contralateral lower-extremity muscle activation patterns, strengths, and durations for the balance tasks were enhaced during stimulation. These results suggest that thalamic stimulation improved this patient's balance by reducing tremor in the contralateral extremities and by increasing burst duration and magnitude of the tibialis anterior, which functions as the postural prime mover for the step initiation and balance tasks.