We reviewed 88 pathologically proven cerebellar infarcts, examining the entire thoracocervical arterial system (including the spinal part of the vertebral artery, the intracranial arteries, and the heart) in all cases. For 50 infarcts, we found an arterial occlusion. The intracranial part of the vertebral artery was involved in 38 infarcts (76%), the basilar artery in 20 infarcts (40%), and a cerebellar artery in 12 infarcts (24%). Eight infarcts were due to bilateral distal vertebral artery occlusions. For the 50 infarcts, the cause of the occlusion was atherosclerosis in 28 (56%) and a cardiac embolism in 12 (24%). For the remaining 38 infarcts, we found no arterial occlusions on postmortem examination. Of these 38 infarcts, 26 (68%) were associated with a cardiac source of emboli. For the entire group of 88 infarcts, atherosclerosis was the cause in 31 (35%), while a cardiac embolism was proven or presumed in 38 (43%). Dissecting aneurysms, atherosclerotic artery-to-artery embolism, or hemodynamic mechanisms could have been responsible for a few infarcts. We conclude that cerebellar infarcts often arise from cardiogenic embolism. (Stroke 1990;21:1299-1305)