Background: Deep brain stimulation of the subthalamic nucleus (STN-DBS) is a very effective surgical procedure for Parkinson's disease. It significantly improves cardinal parkinsonian symptoms as well as levodopa-induced dyskinesia. Interestingly, STN-DBS can also provoke or exacerbate dyskinesia. In the present study, stimulation-induced dyskinesia (SID) was found in the early stage (less than 1 month) after STN-DBS in some patients. The aim was to discuss this interesting phenomenon. Methods: Side effects of each electrode contact were tested at 9.0 +/- 3.8 days (range, 3-16 days) after STN-DBS, and 40 contacts of 16 electrodes ( 15 patients) were found to induce dyskinesia. The location of these contacts was calculated in the postoperative magnetic resonance imaging, and was compared to the positions of active contacts and dorsal margin of the subthalamic nucleus (STN). Results: Most SID at the threshold manifested as repetitively dystonic involuntary movement, and the most common site was the contralateral lower limb (27/40, 67.5%). The mean location of the 40 contacts with SID was 11.9 +/- 0.9 mm lateral, 0.4 +/- 1.7 mm anterior, and 1.8 +/- 1.9 mm inferior to the midcommissural point. The point was located inferior to the dorsal margin of the STN (p = 0.01, t tests), and no significant difference was found between this point and the location of active contacts (p > 0.05, t tests). Conclusion: In the early stage after STN-DBS, dyskinesia is easily induced by high-frequency stimulation of the upper portion of the STN, which may predict the best site for chronic stimulation. Copyright (C) 2009 S. Karger AG, Basel