Acute isolated hemiataxia is in most cases due to infratentorial (cerebellar) stroke. It has only twice been described in supratentorial stroke--namely, after thalamic infarction and a capsular haemorrhage. Three patients with isolated hemiataxia after a supratentorial brain infarct are described. These patients were seen in a period of five years during which 899 patients with a first supratentorial brain infarct were registered. Clinically the hemiataxia was of the cerebellar type. In two patients, CT and MRI showed a small, deep (lacunar) infarct restricted to the posterior limb of the internal capsule, a site not previously reported in isolated hemiataxia. The third patient had a small, deep (lacunar) infarct in the thalamus extending into the adjacent posterior limb of the internal capsule. Isolated hemiataxia after a supratentorial brain infarct is a very rare clinical stroke syndrome. The cerebellar type hemiataxia was most likely caused by interruption of the cerebellar pathways at the level of the internal capsule. Our cases confirm prior observations that the cerebellar pathways run through the posterior part of the posterior limb of the internal capsule separately from the motor and sensory pathways.