The difference in stroke causes between younger and elderly stroke patients may largely depend on differences in the cause of cortical ischaemic stroke, the pathogenesis in lacunar ischaemic stroke being more homogeneous. We therefore compared the vascular risk factor profile and stroke causes between 60 ischaemic stroke patients of 50 years or less and 756 patients older than 50 years, in relation to these two ischaemic stroke subtypes. The stroke causes were classified as small-vessel occlusion, large-vessel atherosclerosis, cardioembolism and as rare definite causes (such as dissection, vasculitis, and coagulation disorders). The rare definite stroke causes were significantly more frequent among young patients (15 vs. 3%, odds ratio 6.2; 95% confidence interval, CI, 2.8–13.6). All these young patients had a cortical stroke. The whole group of lacunar stroke patients (young and old) had significantly less frequently rare definite stroke causes than the whole group of cortical stroke patients (1 vs. 5%; odds ratio 0.22; 95% CI 0.07–0.71). Young patients have more varied stroke causes than older patients, but this is largely confined to cortical stroke patients. Our data suggest that cardiac and carotid embolism, and other rare definite disorders are unlikely stroke causes in young patients with a lacunar str