It has been suggested in the literature that atherosclerosis is a common causal pathway of cognitive impairment and late-onset depression, which may explain their co-occurrence in old age. In both the 'Leiden 85-plus Study' and the literature, strong evidence is found for a causal relationship between atherosclerosis and cognitive impairment, but there is less evidence for a causal relationship between atherosclerosis and late-onset depression. In the 'Leiden 85-plus Study', cognitive impairment was a risk factor for the development of late-onset depression, but depression in old age did not predict cognitive decline. This means that the prevention of atherosclerosis might prevent cognitive impairment and hence late-onset depression in old age.