We identified three factors explaining behavior in the MCI group: a depression, a psychosis, and an agitation syndrome. Similar factors were found in AD, but the order: an agitation, a depression, and a psychosis syndrome, respectively, and the structure differed slightly. Diurnal rhythm disturbances and frontal lobe symptoms loaded with the depression syndrome in MCI and in AD they loaded with the agitation syndrome. Behavioral syndromes correlated in AD, but not in MCI, and the prevalence and severity of the behavioral syndromes were higher in AD than in MCI, except for the severity of the depression syndrome.