Six patients had isolated hemiataxia and ipsilateral sensory loss, as a manifestation of thalamic infarction in the thalamogeniculate territory. Acute hemiataxia-hypesthesia was not found in 1075 other patients from the Lausanne Stroke Registry who were admitted during the same period. Stroke onset was progressive in five patients and immediately complete in one. Five patients had an objective sensory loss. In two patients this affected light touch, pain and temperature sense, and in another three light touch, pain temperature, position and vibration sense. One patient had a purely subjective sensory disturbance. The sensory deficit cleared or was clearing although the ataxia persisted in all patients. On lesion mapping on CT or MRI, all patients had involvement of the lateral part of the thalamus (ventral posterior nucleus and ventral lateral nucleus). The presumed causes of stroke were cardioembolism in one patient, posterior cerebral artery occlusion in one patient and meningovascular syphilis in one patient, hypertensive small vessel disease in two patients, and undetermined in one patient. Hemiataxia-hypesthesia is a new stroke syndrome involving the perforating branches to the lateral thalamus, but in which small vessel disease may not be the leading cause.