There is scarce data as to the association between physical activity and the volumes of subcortical brain regions in people with multiple sclerosis (PwMS).To compare the volumetric measures of subcortical brain structures in physically active and insufficiently active PwMS.This cross-sectional study comprised 153 PwMS (39.3 ± 12.0 years, 68.0% female) who had undergone a complete neurological examination, computerized cognitive evaluation and brain MRI (using a high-resolution scanner). MRI volumetric analysis was based on the FreeSurfer image analysis suite. Regions of interest included the hippocampus, amygdala, brain stem, basal ganglia, thalamus, accumbens nucleus, putamen, caudate and pallidum. Two MRI metrics, total volume (mm3) and estimated percentile of the subcortical region according to adjusted normative population, were calculated for each individual and brain region. Based on scores obtained from the Godin Leisure-Time Exercise Questionnaire, the cohort was subsequently divided into two groups, physically active (n = 77) and insufficiently active (n = 76).The left hippocampus estimated percentile point significantly differentiated between active and insufficiently active PwMS (48.5 (S.D. = 32.2) vs. 36.4 (S.D. = 29.8); p = 0.004), even after controlling for disability (p = 0.011) and cognition (p = 0.021). The right hippocampal estimated percentile point was also significantly different between groups (46.7 (S.D. = 30.6) vs. 34.6 (S.D. = 30.8); p = 0.004). Subcortical volume of the right hippocampus explained 19.4% of the variance between the groups (p = 0.008), even after controlling for disability (p = 0.013) and cognition (p = 0.020).Our results provide evidence that PwMS who regularly participate in leisure-time physical activities maintain their hippocampal volume, regardless of their disability and cognitive capabilities.