OBJECTIVE: To evaluate the differences between early-onset subcortical vascular cognitive impairment (EO-SVCI) and late-onset subcortical vascular cognitive impairment (LO-SVCI) with regard to pathologic burden, structural changes, and cognitive function. METHODS: We prospectively recruited 142 patients from a single referral center. Patients were divided into EO-SVCI (n = 30, age at onset 65 years) and LO-SVCI (n = 112, age at onset ≥ 65 years) groups. All patients underwent neuropsychological tests, 3T brain MRI, and [(11)C] Pittsburgh compound B (PiB)-PET. We compared pathologic burden such as small vessel disease and amyloid burden; structural changes such as structural network, cortical thickness, and hippocampal volume; and cognitive function between EO-SVCI and LO-SVCI. RESULTS: EO-SVCI patients had more lacunes, while LO-SVCI patients had higher PiB standardized uptake value ratios. EO-SVCI patients exhibited more severe structural network disruptions in the frontal area, while LO-SVCI patients exhibited more severe cortical and hippocampal atrophy. Although disease severity did not differ between the 2 groups, frontal-executive dysfunction was more severe in EO-SVCI patients. CONCLUSIONS: EO-SVCI patients showed more vascular related factors, while LO-SVCI patients exhibited more Alzheimer disease-related characteristics. The greater number of lacunes in EO-SVCI might account for the more severe frontal network disruption and frontal-executive dysfunction, while the greater amyloid burden in LO-SVCI might account for the more severe cortical and hippocampal atrophy. Our findings suggest that the age at onset is a crucial factor that determines distinct features in SVCI patients, such as pathologic burden, structural changes, and cognitive function.