Background <p>In this research, we extend our initial study in 2016 of a distinct cohort diagnosed with autoimmune atypical parkinsonism, assessing the long-term effects of immunotherapy over a decade.</p> Objective <p>To study the long-term effects of immunotherapy in patients with autoimmune atypical parkinsonism over 10 years.</p> Design <p>Retrospective Observational Study Design</p> Study Setting <p>The study was carried out at the Department of Neurology at Amrita Institute of Medical Sciences, Kochi, Kerala. The cohort described in our previous study were followed up using data from EMR or by telecommunication.</p> Measurements <p>The authors utilized 9q-mRS scores to assess the disability scores and Kaplan-Meier life tables, using months as the time scale, to estimate the survival of patients with autoimmune atypical parkinsonism who underwent immunotherapy.</p> Results <p>Six out of 10 patients expired, but they experienced a good improvement in their 9q-mRS scores during their treatment. Out of the 4 surviving patients, 3 exhibited outstanding responses to immunotherapy while one maintained stable 9q-mRS over an extended period. Kaplan-Meier survival analysis revealed a mean survival time of 74.7 months and a median of 68 months, with 40% of cases censored.</p> Conclusions <p>Immunotherapy significantly improved the disability scores in patients with autoimmune atypical parkinsonism.</p>