Hypertension is one of the most important risk factors for stroke. However, it is less clear what stroke subtypes have particulary high relative risks associated with treated hypertension. On theoretical grounds, lacunar infarction syndromes and primary intracerebral haemorrhage are more likely to fall into this category since their pathogenesis is thought to relate to underlying hypertensive small vessel changes (lipohyalinosis). For lacunar infarction syndromes there is considerable debate as to whether hypertension is actually a more potent risk factor than for all other formms of cerebral infarction combined. In the case of cerebral haemorrhage, there have been very few studies performed in the post-CT scan era and hence the true relative risk is very poorly quantitated. More epidemiological studies are required to clearly identify stroke subgroups in which hypertension has had the most impact. (Hypertens Res 1994; 17 Suppl. I: S51-S54)