This study explored the efficacy of aerobic training (AT) in mitigating white matter hyperintensity (WMH) progression and whether these changes are sex dependent. This was an exploratory analysis of a randomized controlled trial assessing the effect of AT on cognition in people with vascular cognitive impairment. Participants were randomized to a 6 month AT or usual care (control [CON]) group. A subset completed magnetic resonance imaging to quantify WMH volume. Using an analysis of covariance model, we found a significant sex × group interaction (p = .03). Over the 6 month study, AT females demonstrated greater WMH progression than CON females (p = .05). Among males, there was no significant between-group difference (p = .31). Within the AT group, males demonstrated significantly less WMH progression than females (p = .01) at 6 months. Therefore, the effects of AT on WMH progression may vary by sex; that is, AT may curtail WMH progression in males but not females.