Objectives: Deep brain stimulation (DBS) is the surgical treatment of choice for moderate to severe Parkinson's Disease (PD). However, few studies have assessed its efficacy in severe PD as defined by the modified Hoehn and Yahr scale (HY). This study evaluates long-term and medication outcomes of DBS in severe PD.; Patients and methods: We retrospectively collected the data of 15 patients from 2008 to 2014 with severe PD treated with DBS. Retrospective assessment with the modified Hoehn and Yahr scale and motor subset of the Unified Parkinson's Disease Rating Scale (UPDRS III) were used to objectively track severity and motor function improvement, respectively. Levodopa equivalence daily doses (LEDD), number of anti-PD medications and number of daily medication doses were used to measure improvements in medication burden. Data was evaluated using univariate analyses, one sample paired t-test, two sample paired t-test, and Wilcoxon signed-rank test.; Results: The mean post-operative follow-up was 44.63 months, average age at diagnosis and the average age at time of DBS was 51.3 years and 61.5 years, respectively, and the time from diagnosis to treatment was 13.2 years. Significant decreases were seen in UPDRS III scores (pre-op = 44.533; post-op = 26.13; p = 0.0094), LEDD (pre-op = 1679.34 mg; post-op = 837.48 mg; p = 0.0049), and number of daily doses (pre-op = 21.266; post-op 12.2; p = 0.0046). No significant decrease was seen in the number of anti-PD medications (pre-op = 3.8; post-op = 3.2; p = 0.16).; Conclusion: Following DBS, severe PD patients demonstrated significant improvements in motor function and medication burden during long-term follow-up. We believe our results prove that DBS is efficacious in the management of severe PD, and that further research should follow to expand DBS criteria to include severe disease.