Twenty-two patients with Parkinson's disease were treated by implanting electrodes in the subthalamic nucleus. The follow-up evaluation was conducted at one (22 patients) and two years (9 patients). Significant improvement in the Unified PD Rating Scale scores was found. Tremor diminished 100% in the on drug/on stimulation and 70% off drug/on stimulation state. Rigidity decreased by 68% in the on drug/on stimulation and by 52% in off drug/on stimulation state. Subthalamic stimulation is reliable.