Loss of vascular smooth muscle cell (VSMC) function is a hallmark of vascular disease. VSMCs become increasingly dysregulated, apoptotic, and senescent as we age. Sirtuin 1 (SirT1) is a deactylase that regulates substrates associated with stress mitigation, metabolism, and aging. Our aim was to examine the role of SirT1 in vascular aging and the function this protein plays in the context of cellular response to stress and senescence. We compared endogenous SirT1 expression in young and old human donors. Human VSMC (HuVSMC) from donors ranging in age from 12 to 88 (n = 14) were isolated and cultured. In cultured HuVSMC the levels of endogenous SirT1 were examined by Western blot analysis. We found that endogenous SirT1 protein expression inversely correlated with donor age. Additionally, we demonstrated that age-related loss of SirT1 correlated in functional deficits, diminished stress response, reduced capacity for migration, and proliferation and increased senescence. Manipulation of SirT1 levels in young cells confirmed the role of SirT1 in cellular migration and proliferation capability. Furthermore, we demonstrated that age-related loss of SirT1 was associated with the induction of VSMC senescence. With correlation to symptomatic disease, we demonstrated a significant difference in SirT1 levels from HuVSMC isolated from aged arteries that were occluded with atherosclerotic lesions (n = 7), compared with patent sections of the same artery. Having demonstrated that endogenous SirT1 is lost with age, which correlates with a loss of capacity for vascular repair, our data explain one of the molecular changes that occurs in the aged vasculature.