Embolic and thrombotic infarction in the territory of the posterior cerebral artery (PCA) is described with emphasis on the stroke and cerebrovascular features rather than special neurological syndromes. Of 47 cases of obstruction at the distal bifurcation of the basilar artery, 43 (95%) were consistent with embolism. The clinical categories and pathological findings are presented. Local embolism, vertebral distal-stump embolism, the dynamics of hemorrhagic infarction and embolus-in-transit are briefly described. The prodromal manifestations of PCA thrombotic occlusion include photopsias, hemianopic blackouts, headache, transient episodes of numbness, episodic lightheadedness, spells of bewilderment and rarely tinnitus. Recognition of these may allow prevention of a stroke. Prodromal photopsias did not closely resemble the scintillating displays of migraineurs. When the stroke occurred, visual complaints usually predominated. A sensory deficit occurred in one-third of cases. In 25 cases of memory impairment the dominant hemisphere was involved in 24. The kinds of visual hallucinations, simple and formed, are described.