To determine the adaptive capability of saccadic eye movements, and its association with enduring saccadic dysmetria in cerebellar and lateral medullary infarction (LMI), we investigated saccadic accuracy and adaptation in 15 patients with cerebellar or lateral medullary infarction, compared with those of 7 patients with diffuse cerebellar atrophy and 11 normal subjects. Saccade adaptation was elicited by a 37.5% backward target step during the primary saccade in both horizontal directions. Horizontal preadaptive saccadic gains were decreased in patients with cerebellar infarction, and contralesionally in patients with LMI. In contrast, adaptive saccadic gain change was reduced in patients with diffuse cerebellar atrophy and cerebellar infarction. Saccadic hypometria and reduced saccadic adaptability were dissociated in the majority of the patients with cerebellar infarctions; seven of the eight patients with cerebellar infarction showed saccadic hypometria and only three of them showed reduced saccadic adaptation, uni- or bilaterally in two with bilateral infarctions and ipsilesionally in one with unilateral infarction. The most commonly affected structure on MRI was the cerebellar hemisphere in the patients either with saccadic hypometria or with reduced saccadic adaptation. All patients with unilateral LMI exhibited normal saccadic gain adaptation in both directions, including those patients with enduring saccadic ipsipulsion. Our results suggest that the cerebellar hemispheres as well as the dorsal vermis and fastigial nucleus may be involved in the control of saccadic accuracy and adaptation. Reduced saccadic adaptation and persisting dysmetria are not tightly linked to each other in the cerebellar or lateral medullary lesions.