Deep hemispheric or brainstem small infarcts can lead to atypical lacunar syndromes. Unilateral internuclear ophthalmoplegia (INO) and cerebellar ataxia has not been reported previously. A 57-year-old hypertensive female presented with bilateral appendicular and left truncal cerebellar ataxia and right INO. Cranial MRI showed a right paramedian infarct of lacunar size located in the tegmentum of caudal mesencephalon. At this level the involvement of medial longitudinal fascicle (MLF) led to right INO and the lesion of brachium conjunctivum caused the bilateral cerebellar ataxia. Ipsilateral involvement of both cerebellofugal fibers, before and after decussation, was responsible for bilateral cerebellar ataxia. Copyright (C) 2001 S. Karger AG, Basel.