Of 225 patients referred to a dementia clinic, depression occurred in 31 (70%) of 44 patients not thought to be demented, six (24%) of 25 with cognitive impairment not severe enough to warrant the label dementia, and 24 (15%) of 156 with various forms of dementia, including 19 (19%) of 99 with Alzheimer-type dementia. Follow-up over three years has shown that 16 (57%) of 28 of the depressed, nondemented patients went on to develop frank dementia. Thirteen of these 16 had some sign, often subtle, of organic neurologic disease. Depressed elderly patients with any of the following are at high risk to develop dementia: evidence of cerebrovascular, extrapyramidal, or spinocerebellar disease; a modified Hachinski ischemic score of 4 or greater; a Mental Status Questionnaire score under 8; a dementia behavior score of 7 or higher; or confusion on low doses of tricyclic antidepressants. Dementing illnesses can present as depression with relatively little cognitive impairment.