Scintigraphy with radiolabeled metaiodobenzylguanidine (MIBG) enables the visualization and quantification of functionally intact adrenergic neurons and cells. In Parkinson disease, MIBG uptake of postganglionic cardiac sympathetic neurons is grossly reduced at an early stage of the disease in almost all patients with a clinical severity score of Hoehn and Yahr II or higher. Based on the meta-analysis of studies with a total of 246 cases of Parkinson disease and 45 cases of multiple system atrophy, the overall sensitivity to positively identify patients with Parkinson disease was 89.7%, and the specificity to discriminate them from patients with multiple system atrophy was 94.6%. Quantification of cardiac MIBG uptake is a valuable tool to identify patients with Parkinson disease and to discriminate them from other neurodegenerative disorders early in the course of the disease.