Dementia with Lewy bodies has been called a variant of Alzheimer’s disease, but Ballard et al. (p. 843) report differences in the neuropathological basis of psychiatric symptoms. Depression, delusions, and hallucinations were assessed yearly in patients with dementia. After the patients died, autopsies were conducted to quantify neuritic plaques, neurofibrillary tangles, and Lewy bodies; Lewy body dementia was diagnosed in 112 patients and Alzheimer’s disease in 90 patients. All three psychiatric symptoms were more common in Lewy body dementia, and greater Lewy body pathology was related to persistent delusions and persistent visual hallucinations. Conversely, the presence of fewer tangles correlated with persistent visual hallucinations. Patients with Lewy body dementia who had extensive tangles were more similar clinically to patients with Alzheimer’s disease and had fewer neocortical Lewy bodies. Depression was unrelated to brain pathology. The different neuropathologies underlying hallucinations and delusions in the two patient groups suggest their responses to treatment are also likely to differ.