Reduced cardiac uptake of 123I-metaiodobenzylguanidine (MIBG) is considered to represent dysfunction of the postganglionic neurons of the cardiac sympathetic nervous system. Evidence indicates that cardiac uptake of 123I-MIBG is decreased in patients with idiopathic Parkinson's disease (IPD), dementia with Lewy bodies (DLB) and pure autonomic failure (PAF), which have common pathological features with Lewy body formation. In the present article, we review previous reports that determined heart-mediastinum (H/M) ratios in early and delayed images of patients with progressive supranuclear palsy (PSP), corticobasal degeneration (CBD) and multiple system atrophy (MSA) in comparison to those of IPD and controls. The majority of reports suggest that H/M ratios of patients with PSP, CBD and MSA are comparable to those of controls, while H/M ratios of patients with IPD are significantly reduced. This reduction seen in IPD may reflect the loss and/or dysfunction of postganglionic cardiac sympathetic nerve terminals. Several authors reported mild reduction of 123I-MIBG uptake in patients with MSA and PSP. However, no degeneration of postganglionic neurons of the cardiac sympathetic nervous system has been detected in patients with these diseases. These results indicate that cardiac 123I-MIBG uptake is a sensitive tool with which to differentiate IPD from neurodegenerative diseases with extrapyramidal symptoms such as PSP, CBD and MSA.