Subthalamic nucleus (STN) lesions or high-frequency stimulations could improve parkinsonian symptoms in monkeys treated by MPTP. We have applied the procedure of chronic stimulation to the STN in severely disabled parkinsonian patients. This article presents the case of the first patient operated on bilaterally. Bilateral STN stimulation has greatly improved akinesia and rigidity. The benefit was maintained < or = 15 months after surgery. Unilateral stimulation induced motor effects mainly in contralateral limbs. Further studies are needed to evaluate the value of this procedure in the treatment of Parkinson's disease.