Lateral medullary infarction: prognosis in an unselected series. We describe the acute and long-term prognosis in 43 patients with lateral medullary infarction (LMI) collected from a population-based stroke registry from 1982 to July 1988. Mean age was 63.9 years and median time of follow-up was 33 months. In the acute phase, 5 patients (11.6%) died from respiratory and cardiovascular complications and 2 new strokes occurred, both in the posterior circulation. During follow-up, recurrent vertebrobasilar territory strokes occurred in only 2 patients (a rate of 1.9% per year). The mechanisms of stroke were vertebral artery (VA) branch occlusion, causing a medial medullary syndrome, and basilar artery thrombosis propagating from a contralateral, distal VA stenosis. In the acute phase of LMI, respiratory and cardiovascular events, presumably caused by autonomic dysfunction related to the lateral medullary lesion, are the major hazards. Recurrent posterior circulation strokes were uncommon during follow-up. 