We studied 208 consecutive outpatients with dementia (diagnosis based on DSM-III-R criteria; mean [SD] age of 77.0 [8.0] years; study period: September 2011-August 2012). Delusional jealousy was defined as a false belief derived from a pathological jealousy that makes the patient believe that his or her spouse is unfaithful. The prevalence of delusional jealousy was compared between Alzheimer's disease, dementia with Lewy bodies, and vascular dementia. Patients with and without delusional jealousy were compared in terms of general characteristics. In addition, each patient with delusional jealousy and their primary caregivers were interviewed about the clinical features of the syndrome