Ageing and atherosclerosis are associated with oxidative stress. Mitochondrial redox function declines with ageing. Here we tested whether ageing LDL receptor knockout mice (LDLr-/-) develop spontaneous atherosclerosis and whether mitochondrial reactive oxygen species (mtROS) correlate with atherosclerosis. Compared with young mice, aged LDLr-/- mice exhibited 20-fold larger aortic lesion size, although the plasma cholesterol levels did not vary between age groups. The lesion sizes increased exponentially from 3 to 24months of age (r=0.92, p=0.0001) and were correlated with mtROS across the age range (r=0.81, p=0.0001). Thus, LDLr-/- mice develop spontaneous diet-independent atherosclerosis, that advances exponentially with ageing. We propose that age related increases in mtROS contribute to accelerate atherosclerosis development in hypercholesterolemic mice. © 2017 Elsevier Inc.