One hundred consecutive outpatients with dementia were prospectively studied to investigate the diagnoses of dementing diseases and to correlate these diagnoses with socioeconomic status and with education. Alzheimer disease was the most common cause of dementia (54%), followed by vascular dementia (20%). Eight patients presented with potentially reversible causes of dementia. These frequencies are similar to those reported by case register studies from Western Europe and the United States. We did not find differences in the frequencies of the dementing diseases according to socioeconomic status or education. Alzheimer disease was the most common cause of dementia in all socioeconomic classes. Potentially reversible dementias, vascular dementias, and other secondary dementias were not more frequent in the lower socioeconomic strata. There was a trend to a higher frequency of vascular dementia among patients with less education, but this was not statistically significant.