Objectives: We hypothesize that the regional pattern of blood flow reduction in the brain is different between tremor-dominant Parkinson’s disease (PD) and postural instability gait difficulty (PIGD)dominant PD. We therefore investigated the association of phenotypes in untreated PD with brain perfusion on SPECT using three-dimensional stereotactic surface projection (3D- SSP) technique. Patients and methods: Thirty-three patients who had PD without dementia (12 men and 21 women with a mean age of 67.1 ± 6.4 years) were included in this study. Their symptoms were rated using the Unified Parkinson’s Disease Rating Scale (UPDRS). Patients were grouped in two phenotypes: tremor and PIGD-dominant groups based on UPDRS components. Around the same time, all patients were examined by N-isopropyl-p[123I] iodoamphetamine single photon emission computed tomography (123I- IMP SPECT), and obtained images were analyzed with 3D- SSP using an image-analysis software, NEUROSTAT. Data on brain surface perfusion extracted by 3D- SSP analysis were compared between the PD patients and the normal control group. The same comparisons were made for subgroups of PD patients. Results: Cerebral perfusion was decreased at the anterior cingulate cortex and primary visual cortex of the PD patients, and especially by the pixel-by-pixel comparison, perfusion was significantly decreased at the right anterior cingulate cortex compared with the normal controls. In the PIGD-dominant group, more severe hypoperfusion was seen at the same regions. In the tremor-dominant group, significant hypoperfusion was not seen compared with the normal controls. Conclusions: The regional pattern of blood flow reduction in the brain was found to be different between tremor-dominant PD and PIGD-dominant PD. These regional differences were considered to suggest different and disease-specific combinations of underlying pathophysiological and neurochemical processes. Objectives: We hypothesize that the regional pattern of blood flow reduction in the brain is different between tremor-dominant Parkinson’s disease (PD) and postural instability gait difficulty (PIGD) dominant PD. We therefore investigated the association of phenotypes in untreated PD with brain perfusion on SPECT using three-dimensional stereotactic surface projection (3D-SSP) technique. Patients and methods: Thirty-three patients who had PD without dementia (12 men and 21 women with a mean age of 67.1 ± 6.4 years) were included in this study Their symptoms were rated using the Unified Parkinson’s Disease Scale (UPDRS). Patients were grouped in two phenotypes: tremor and PIGD-dominant groups based on UPDRS components. Around the same time, all patients were examined by N-isopropyl-p [ 123I] iodoamphetamine single photon emission computed tomography (123I-IMP SPECT), and images were analyzed with 3D-SSP using an image-analysis software, NEUROSTAT. Data on brain surface perfusion extracted by 3D-SSP analysis were compared between the PD patients and the normal control group. The same comparisons were made for subgroups of PD patients. Results: Cerebral perfusion was decreased at the anterior cingulate cortex and primary visual cortex of the PD patients, and especially by the pixel-by-pixel comparison, perfusion was significantly decreased at the right anterior cingulate cortex compared with the normal controls. In the PIGD-dominant group, more severe hypoperfusion was seen at the same regions. In the tremor-dominant group , significant hypoperfusion was not seen compared with the normal controls. Conclusions: The regional pattern of blood flow reduction in the brain was found to be different between tremor-dominant PD and PIGD-dominant PD. These regional differences were considered to suggest different and disease -specific combinations of underlying pathophysiological and neurochemical processes.