Objective To investigate the distribution characteristics of enlarged perivascular spaces (EPVS) in patients with Alzheimer's disease (AD), Parkinson's disease (PD), and high blood pressure (HBP) and their clinical significance, and to deepen the radiological understanding of this common cerebral small vessel disease.Methods A retrospective study was performed on equal numbers (n=100) of age-and gender-matched patients with AD, PD, and HBP who were admitted to our hospital from January 2012. An equal number of healthy middle-aged and elderly volunteers were used as control (N). All the subjects received 3.0-T magnetic resonance imaging of the brain. Based on the T2-weighted and fluid attenuation inversion recovery images in the centrum semiovale (CSO), basal ganglia (BG), and hippocampus (HC), the number and distribution characteristics of EPVS were compared between the four groups. The correlation of EPVS number with age in all patients and the mini-mental state examination (MMSE) score in AD patients was analyzed.Results There were significant differences in anatomical distribution of EPVS in the CSO and BG between the four groups (all P<0.001). The AD, HBP, and PD groups had significantly larger numbers of EPVS than the control group (all P<0.001). In the CSO, the AD group had a substantially larger number of EPVS than the other three groups (AD=11.23, HBP=8.97, PD=7.88, N=3.00). In the BG, the HBP group had a substantially higher number of EPVS than the other three groups (HBP=7.21, PD=5.85, AD=4.87, N=2.95). In the HC, there was no significant difference in the number of EPVS between the AD, HBP, and PD groups. The percentage of CSO-EPVS in the whole brain was substantially higher in the AD group than the other three groups (AD=69.41%, HBP=54.75%, PD=57.49%, N=46.35%). Particularly, the AD group had a significantly higher percentage of CSO-EPVS than the HBP group (P<0.001). According to the results of Spearman correlation analysis, the EPVS number was positively correlated with age in the AD, HBP, and PD groups (r_s=0.34, 0.41, 0.49, all P<0.01), while there was no such correlation in the control group. In the AD group, the EPVS number was negatively correlated with the MMSE score in the CSO (r_s=-0.251, P<0.05), while there was no such correlation in the BG.Conclusions EPVS in AD and HBP patients are mainly located in the CSO and BG, respectively, while there is no regional distribution for EPVS in PD patients. The number of EPVS increases with age in AD, HBP, and PD patients. In AD patients, the more EPVS in the CSO, the worse cognitive function. The EPVS number may be of great value in predicting the degree of cognitive impairment.