Using a standard protocol including MRI and magnetic resonance angiography (MRA), we studied 28 consecutive patients, all with an acute infarct in the lower brainstem. MRI patterns above and below the inferior olivary nucleus enabled identification of six topographical types of infarct: small midlateral, dorsolateral, inferolateral, large inferodorsolateral, dorsal and paramedian infarcts. Small midlateral, dorsolateral, inferolateral and inferodorsolateral infarcts were the most common types and were associated with Wallenberg's syndrome, with specific clusters and severity of neurological features in each of the four groups. Dorsal infarcts were both anatomically and clinically overshadowed by a constant associated cerebellar infarct in the posterior inferior cerebellar artery (PICA) territory. Paramedian infarction led to crossed tongue and sensorimotor hemiplegia, while a patient with an almost complete hemimedullary infarct had unusual ipsilateral sensory and motor disturbance due to lesion extension toward the upper spinal cord. A coexisting cerebellar infarct was present in 36% of the cases, but was never found with midlateral or inferolateral infarct. Angiography showed an embolic occlusion of the PICA in five patients (18%), four of them having dorsal or dorsolateral infarct. Atheromatosis was by far the most frequent stroke aetiology (72%), with intracranial vertebral artery tight stenosis or occlusion in 28% of the cases and in 75% of the cases with large inferodorsolateral infarct. Vertebral artery dissection and cardioembolism accounted each for 14% of the cases, the latter being associated with dorsal infarct. Our study shows that differences in topographical patterns of infarction in the lower brainstem probably reflect differences in aetiopathogenic mechanisms.