Contemporary research has shown that delusions are often the product of identifiable neurologic disease, particularly when the delusions have a specific theme or are confined to one topic--monosymptomatic or content-specific delusions. Although these delusions are considered rare, some of them can be found at high rates in certain populations and settings. The literature on several classes of content-specific delusions (misidentification, sexual, and somatic) is critically reviewed. The review demonstrates that when adequate diagnostic workups are conducted, a high proportion of such delusions are found to have a neurologic basis. Lesions of the frontal lobes and the right hemisphere are shown to be critical to the development and persistence of many content-specific delusions.