STN stimulation has a demonstrated effect on akinesia and rigidity and allows to significantly reduce medication. Pallidotomy is commonly targeted on the internal globus pallidus (GP) to reduce dyskinesias and parkinsonian signs. In a patient, with an unilateral lesion restricted to the right external GP, we performed STN stimulation by means of two quadripolar electrodes. Before SIN the patient bad an UPDBS motor score of 40 in off-state and 23 in on-state (42% of improvement). the Hoehn and Yahr stage was JV in offstate and BJ in on-state. The levodopa equivalent daily dosage (LEDD) was 1050. Bilateral STN implant was performed. Successful targeting of STN was confirmed by MRl. Pet-operatively and in the immediate postoperative period, the expected improvement of parkinsonian signs on the left side was not observed with high frequency stimulation of the right STN (homolateral to pallidotomy), but it was observed as expected, on the right side with stimulation of the left STN. 'Ibe patient was discharged with a combination of bilateral STN stimulation and medication (LEDD = 750). One month after the implant the patient obtained a satisfatory motor control without dyskinesias. The UPDRS motor score was 48 with stimulation off and 18 with stimulation on (63% of improvement). No evident difference in improvement was observed between tight and left side. Side effects consisted only in dysatthria related to stimulation. The present case shows that a preexisting unilateral lesion of external GP may interfere with the immediate observation of an efficacy of STN stimulation on the lesioned side. Chronic STN stimulation was nevertheless efficacious on both sides, as evaluated one month following the implant. Partially supported by grant 3/00-05-3006.97 of Swiss National Foundation for Scientific Research.