White matter lesion (WML), one of the sequelae of cerebral hypoperfusion, accumulates with age. This study sought to investigate the relationship between cerebral blood flow (CBF) and WML severity with age in asymptomatic adults. We found that WML scores were strongly associated with WM CBF, suggesting that WM CBF might be an effective indicator for severity of WMLs. We also found that the WM CBF increased with age, consistent with the greater WM cerebrovascular reactivity response in elderly individuals. In addition, our findings of ascending WM CBF cut-off values revealed that the risk of developing WML increases with age.