Alzheimer's disease (AD) is associated with cognitive and functional impairment as well as neuropsychiatric complications, including psychotic symptoms such as delusions and hallucinations. Recent studies strongly suggest that delusions should be separated from hallucinations. While AD with delusions is a phenotypically distinct from AD without delusions, subtypes of delusions may also define further distinct clinical entities. There has been also considerable debate as to whether delusions in patients with AD differ etiologically, phenomenologically, and therapeutically from delusions in other primary psychiatric illnesses. In other words, whether they are caused by changes to key areas of the brain that have been linked to the presence of delusions. This has led to speculation that these symptoms may respond better to certain drugs such as cholinesterase inhibitors. Integrating the epidemiology, clinical phenomenology, neuropathological and genetic literature for delusions in AD allows us to speculate on pathophysiology and is essential to making progress in the area of delusions in AD.