Background Subthalamic deep brain stimulation (STN-DBS) has been shown to be effective in the treatment of Parkinson's disease. The site for permanent stimulation is still in debate. This study aimed to assess the position of active contacts in relation to the subthalamic nucleus. Methods We reviewed the location of 40 electrodes in 34 patients who underwent STN-DBS. The position of electrode was evaluated by postoperative magnetic resonance imaging (MRI). The position of active contacts was compared with the subthalamic nucleus (STN) determined by intraoperative electrophysiological mapping and postoperative MRI. Results The average position of the 40 active contacts was (11.7+/-1.2) mm lateral, (0.6+/-1.3) mm anterior, and (0.7+/-1.4) mm vertical to the midcommissural point. The dorsal margin of the STN was (11.6+/-1.1) mm lateral, (0.2+/-1.1) mm anterior, and (1.3+/-1.1) mm vertical to the midcommissural point. When compared with the dorsal margin of the STN, the active contacts were located more dorsally (P=0.033) and anteriorly (P=0.012), no significant difference was found in the lateral direction (P=0.107). When compared with the position of the STN, 26 (65%) of active contacts were located in the region dorsal to the STN, only 13 (32.5%) were located in the upper two-thirds portion of STN. Conclusions The site for permanent stimulation appears to be in the subthalamic region dorsal to the STN, close to the dorsal margin of the STN. Besides the dorsal portion of the STN, other structures such as fields of Forel H and zona incerta may also be involved in the therapeutic benefit of deep brain stimulation. Chin Med J 2009;122(20):2419-2422