Background: For quality analysis, we applied the Six Sigma concept to define quality indicators and their boundaries as well as to compare treatment-dependent outcome data of deep brain stimulation (DBS) of the subthalamic nucleus (STN) in patients with Parkinson-s disease (PD). Methods: The Unified Parkinson Disease Rating Scale (UPDRS) III with on medication and on stimulation, the reduction of daily levodopa equivalence doses (LED), and the stimulation amplitude 1 year after surgery were registered. Regarding the results of the EARLYSTIM study, sigma values for applicable studies were calculated and compared. Further, the impact of perioperative conditions on patients- outcomes was analyzed. Results: Forty-one studies with 2184 patients were included. The bleeding risk was 1.36%. In median, UPDRS III on/on improved by 19.9% while the LED was reduced by 45.2%. The median stimulation amplitude was 2.84 V. With the Six Sigma principle, a comparison between different centers was possible. Microelectrode recordings (MER) did not correlate with occurrence of bleedings and did not impact patient outcome. Conclusions: The Six Sigma principle can be simply used to analyze, improve and compare complex medical processes, particularly, the DBS surgery. Based on these data, higher sigma values were reached for clinical improvement in UPDRS III on/on for patients who underwent surgery in local anesthesia with intraoperative test stimulation compared to surgery in general anesthesia. However, the difference was not statistically significant. Application of MER was found to be optional with no increased bleeding risk and no improvement on patient-s outcome.