OBJECTIVE: To assess the efficacy of a progressive aerobic exercise training program on cognitive and everyday function among adults with mild subcortical ischemic vascular cognitive impairment (SIVCI). METHODS: This was a proof-of-concept single-blind randomized controlled trial comparing a 6-month, thrice-weekly, progressive aerobic exercise training program (AT) with usual care plus education on cognitive and everyday function with a follow-up assessment 6 months after the formal cessation of aerobic exercise training. Primary outcomes assessed were general cognitive function (Alzheimer's Disease Assessment Scale-Cognitive subscale [ADAS-Cog]), executive functions (Executive Interview [EXIT-25]), and activities of daily living (Alzheimer's Disease Cooperative Study-Activities of Daily Living [ADCS-ADL]). RESULTS: Seventy adults randomized to aerobic exercise training or usual care were included in intention-to-treat analyses (mean age 74 years, 51% female, n = 35 per group). At the end of the intervention, the aerobic exercise training group had significantly improved ADAS-Cog performance compared with the usual care plus education group (-1.71 point difference, 95% confidence interval [CI] -3.15 to -0.26, p = 0.02); however, this difference was not significant at the 6-month follow-up (-0.63 point difference, 95% CI -2.34 to 1.07, p = 0.46). There were no significant between-group differences at intervention completion and at the 6-month follow-up in EXIT-25 or ADCS-ADL performance. Examination of secondary measures showed between-group differences at intervention completion favoring the AT group in 6-minute walk distance (30.35 meter difference, 95% CI 5.82 to 54.86, p = 0.02) and in diastolic blood pressure (-6.89 mm Hg difference, 95% CI -12.52 to -1.26, p = 0.02). CONCLUSIONS: This study provides preliminary evidence for the efficacy of 6 months of thrice-weekly progressive aerobic training in community-dwelling adults with mild SIVCI, relative to usual care plus education. CLINICALTRIALSGOV IDENTIFIER: NCT01027858. CLASSIFICATION OF EVIDENCE: This study provides Class II evidence that for adults with mild SIVCI, an aerobic exercise program for 6 months results in a small, significant improvement in ADAS-Cog performance.