A brief review of classification in psychiatry from Kraepelin to ICD-10 and DSM-IV reveals that the categorical paradigm inherent in these nosological systems has certain inadequacies when applied to dementia specifically and cognitive impairment in general. There are “outcasts” from these two systems that, with the rapid advances in an understanding of cognitive disorders, expose significant limitations in them. As and when they are revised, serious consideration of a different view, accepting a dimensional paradigm, would contribute to a more inclusive and clinically relevant nosology for dementia and cognitive disorders.