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The over-inhibition of thalamic relay cells by hyperactivity of the internal part of the globus pallidus is a cornerstone of the parkinsonian pathophysiology that leads to a distortion of the thalamocortical dynamics called thalamocortical dysrhythmia (TCD). Here, we present the results of the stereotactic pallidothalamic tractotomy (PTT), which interrupts selectively the enhanced pallidal output to the thalamus in a restricted location in the fields of Forel. This operation represents a reactualization of Spiegel's campotomy. PTT was offered to 41 patients (66.1±8.5 years) suffering from chronic, therapy-resistant Parkinson's disease. It was performed bilaterally in 21 patients. Forty patients displayed mixed, i.e. tremulent and akinetic parkinsonian signs, and seven had drug-induced dyskinesias. One patient had only rest tremor. The evaluation was based on the Unified Parkinson's Disease Rating Scale (UPDRS) scores, comparing the patients' preoperative medicated state with the state at the last postoperative follow-up. We, thus, tested surgical success in terms of superiority to drug treatment. Mean follow-up was 22.4 months with 15 patients followed for >2 years. Mean improvement was 60% (P<0.001) for UPDRS III and 51% (P<0.001) for UPDRS II. Significant improvement (P<0.001) appeared in subscores for tremor (87%), limb akinesia (58%) and axial akinesia (33%). Improvement of postural stability and gait was at the limit of significance (P<0.05). Improvement of hypomimia and hypophonia did not reach statistical significance. Increase of dysarthria was significant (P<0.01). Intake of L-DOPA was reduced significantly and 21 patients were able to stop intake. Median improvement of the Quality of Life score was 67%. Improvement remained, independent of follow-up length. In conclusion, PTT provides a high, stable level of relief to parkinsonian patients whose condition cannot be controlled with pharmacotherapy. The rationale of the surgical therapy is based on a selective extrathalamic regulation of the parkinsonian TCD.