Potential early markers of neurodegeneration such as subtle motor signs, reduced color discrimination, olfactory impairment, and brain perfusion abnormalities have been reported in idiopathic rapid eye movement sleep behavior disorder, a risk factor for Parkinson's disease and Lewy body dementia. The aim of this study was to reproduce observations of regional cerebral blood flow abnormalities in a larger independent sample of patients and to explore correlations between regional cerebral blood flow and markers of neurodegeneration. Twenty patients with idiopathic rapid eye movement sleep behavior disorder and 20 healthy controls were studied by single-photon emission computerized tomography. Motor examination, color discrimination, and olfactory identification were examined. Patients with rapid eye movement sleep behavior disorder showed decreased regional cerebral blood flow in the frontal cortex and in medial parietal areas and increased regional cerebral blood flow in subcortical regions including the bilateral pons, putamen, and hippocampus. In rapid eye movement sleep behavior disorder, brain perfusion in the frontal cortex and occipital areas was associated with poorer performance in the color discrimination test. Moreover, a relationship between loss of olfactory discrimination and regional cerebral blood flow reduction in the bilateral anterior parahippocampal gyrus, a region known to be involved in olfactory functions, was found. This study provides further evidence of regional cerebral blood flow abnormalities in rapid eye movement sleep behavior disorder that are similar to those seen in Parkinson's disease and Lewy body dementia. Moreover, regional cerebral blood flow anomalies were associated with markers of neurodegeneration.