Visual hallucinations are common in patients with dementia with Lewy bodies (DLB), and can also be present in Alzheimer disease (AD). Voxel-based morphometry in 78 patients with AD, half of whom experienced hallucinations, detected specific regions of grey and white matter atrophy associated with hallucinations; the right anterior insula was of core importance. Autopsy of four patients who had experienced hallucinations revealed combined AD and DLB pathology.