A 59-year-old man developed problems with reading and driving. When first examined, he had great difficulty locating and identifying items by sight. Visual acuity was normal, but contrast sensitivity for low spatial frequencies was severely impaired. The peripheral visual fields were moderately constricted with depressed flicker fusion frequencies, more on the right. Color identification was preserved. The difficulties in identifying and locating objects by sight were aggravated by increasing the complexity and multiplicity of the items in the field of vision and by changing the ambient illumination. Intellect and memory were relatively intact, except for difficulty with calculations. Over a 12-year course the visual defects steadily worsened, and eventually memory and language skills failed. Social manners, perseverance, and affect remained normal. Postmortem examination showed cortical atrophy, predominantly posterior, with abundant neurofibrillary tangles and senile plaques. The density of the tangles was correlated with the severity of the atrophy, being highest in the occipitoparietal areas and lowest in the frontal lobes. Alzheimer's disease can preferentially affect the posterior cerebral hemispheres and cause a dementia presenting with, and dominated by, visual disturbances.