The relationship between neuronal activity in subthalamic nucleus (STN) and parkinsonian symptoms was investigated. Thirty-five patients with idiopathic Parkinson's disease (PD) received stereotactic surgical treatment. Microelectrode recording in STN and electromyography (EMG) on the limb contralateral to the surgical side were employed intraoperatively. Single unit firings discriminated from multiple neuronal discharges were recorded, and the correlation between neuronal activity and limb EMG was analyzed. The results showed that there were distinguished characteristics of neuronal discharges in STN and its surrounding areas. Of 346 STN neurons recorded from 36 microrecording trajectories in 35 patients, three patterns of neuronal activities were identified: irregular bursting pattern with a mean frequency of 43.0 ± 11.2 Hz (56%, n = 244); tonic firing pattern with a mean firing frequency of 41.0 ± 12.0 Hz (15%, n = 66); and regular bursting pattern with a mean frequency of 47.0 ± 11.7 Hz (29%, n = 126). The rhythm of regular bursting with the frequency ranging from 3.8 to 6.0 Hz was highly correlated with the frequency of limb tremor measured by EMG (r 2 = 0.66, P < 0.01). These cells were therefore called tremor-related neurons or tremor cells. In particular, 80% tremor cells were located in the medio-superior part of STN. In conclusion, our results suggest that microelectrode recording is a critical technique for electrophysiological localization of the target in treating PD. The tremor-related neuronal activity and movement-related neuronal activity recorded from STN are responsible for the clinical parkinsonian symptoms, suggesting that STN plays an important role in the pathophysiology of PD.