Depression is a risk factor for dementia in general, including Alzheimer’s disease（AD）, its premorbid signs are commonly observed, and the morbidity of depression is higher in dementia patients. Dementia with Lewy bodies（DLB）is considered to have an even higher depression prevalence and premorbid depression rate than other dementias such as AD. This led to depression being listed as a supportive feature in the 2005 criteria for the clinical diagnosis of DLB. However, studies investigating the difference in depression between AD and DLB failed to show consistent results. We examined the Geriatric Depression Scale score, which is designed specifically to rate depression in the elderly, for DLB and AD patients. The scores for DLB patients were twice as high as those for AD patients. There was no correlation between the GDS score and age, sex, or Mini‒Mental Sate Examination scores. Depression‒specific symptoms were more frequent in the DLB group than non‒specific symptoms, while less than one third of DLB patients with very high GDS scores were diagnosed with depression or prescribed antidepressants for depressive symptoms. Other researchers reported that depression of DLB was associated with a higher prevalence of psychiatric symptoms other than major depression, and suggested that depression of DLB might be a part of psychiatric syndrome. There has been no systematic study on the validity or risk of pharmacological therapy, as well as the necessity of intervention, for depression or a high GDS score in DLB. Therefore, intervention must rely on the clinical decision of each doctor.
 In spite of the paucity of current findings, studies on depression of DLB may play a key role in the elucidation of its neuropathology and psychopathology and offer a new view point on understanding depression itself.