A 58 year old hypertensive man suffered an acute right-sided hemiataxia associated with painful hypoesthesia. CT showed an infarct in the territory of the left anterior choroidal artery. The sensory defect involved all the elementary modes, but predominated on pain sensation. The ataxia suggested a cerebellar type of dysfunction, with hypermetria, intentional tremor, dysdiadochokinesia and a positive rebound phenomenon. There was no hemiparesis, no hemianopia, no neuropsychological dysfunction and no oculomotor abnormality. Hemiataxia with hemisensory defect has not been reported in stroke, and it constitutes a new clinical form of lacunar syndrome. The hemiataxia may be related to the finding on single-photon emission computed tomography (SPECT) using 123 I-amphetamine of a crossed cerebellar diaschisis, which may suggest a transneuronal deactivation. This metabolic depression may have been due to involvement of the temporo-parieto-pontine bundle of Türck in the retro and sub-lenticular portion of the internal capsule. The finding of a normal cortical blood flow may explain why no neuropsychological impairment was present, because of the absence of functional deactivation of the cortex by the underlying deep infarct.