The author proposed the terms "diffuse Lewy body disease(DLBD)" in 1984 and "Lewy body disease(LBD)" in 1980. Some Japanese researchers have called DLBD "Kosaka' s disease". On the other hand, "dementia with Lewy bodies (DLB)", which was proposed by the consortium of DLB in 1996, has been sometimes called "Kosaka's disease" by some researchers. Recently DLB, Parkinson disease (PD) and PD with dementia(PDD) are understood within the spectrum of LBD. In this paper the author reviews the concepts of DLBD, DLB and LBD, and discusses on the suggestion of the editorial board of "BRAIN and NERVE" that DLBD or DLB might be called "Kosaka's disease". According to the opinion of the author, DLBD, but not DLB, had better be called "Kosaka's disease", since the term DLB had been proposed based upon the concept of DLBD.