OBJECTIVE: To determine the impact of hepatic dysfunction on the motor manifestations of Parkinson's disease. METHODS: We conducted a retrospective cohort study using data from the Parkinson's Progression Markers Initiative. Liver fibrosis was defined using the Fibrosis-4 score. Our primary outcome was the association of baseline Fibrosis-4 score with the Movement Disorders Society - Unified Parkinson's Disease Rating Scale (MDS-UPDRS) part III score. Additional outcomes were MDS-UPDRS part II, MDS-UPDRS part IV, Hoehn and Yahr stage, and levodopa equivalent daily dose. We used linear regression models to evaluate associations at baseline and 5 years after enrollment. We used linear mixed models to evaluate the association of liver fibrosis with the progression of motor dysfunction. Models were adjusted for demographics, comorbidities, alcohol use, time since Parkinson's disease diagnosis, levodopa equivalent daily dose, and genetic predisposition. RESULTS: We included 360 people with Parkinson's disease with a mean age of 61.8 years (standard deviation 9.7) and 41.1 % women. There was a significant association between liver fibrosis and baseline MDS-UPDRS part III score (β=2.3, 95 % CI: 0.2, 4.5). Liver fibrosis was also correlated with higher interhemispheric signal asymmetry on DAT-SPECT scans in the anterior putamen (p < 0.05 by Wilcoxon rank sum test). There was no correlation with Fibrosis-4 score and any other motor assessment at baseline or after 5 years. Patients with elevated Fibrosis-4 scores had a slower rate of progression in MDS-UPDRS part III scores. CONCLUSION: In people with Parkinson's disease, the presence of comorbid liver fibrosis was associated with more severe motor dysfunction early, but not later, within their disease course.