The association between Parkinson's disease (PD) and body mass index (BMI) has not been established. In this study, we investigated the correlation between BMI and autonomic dysfunction in patients with PD.Clinical features, BMI, cardiac 123I-metaiodobenzylguanidine (MIBG) scintigraphy and the coefficient of variation of the electrocardiographic R–R interval (CVRR) were analyzed in 124 patients with PD who were naïve to anti-parkinsonian drugs.BMI was negatively correlated with early heart-to-mediastinum ratio and CVRR in patients with PD, regardless of disease duration and severity.Autonomic dysfunction and BMI increase were associated with each other. Physicians should consider the possibility of autonomic dysfunction in PD patients with high BMI.