Dementia is a syndrome characterized by the development of multiple cognitive deficits and behavioral changes that leads to impairment of functional activities. There are primary degenerative, progressive and irreversible dementias, and other dementias resulting from a progressive but potentially reversible dementia of secondary origin. To assess the prevalence of cases with a diagnosis of potentially reversible dementia at a Behavioral Neurology Outpatient Unit. A retrospective study based on a review of 340 medical records of patients seen from 1999 to 2009 was conducted. All patients received a thorough diagnostic assessment to verify the etiological hypothesis proposed. Of the 340 patients seen in the study period, 172 (50.5%) were females and 168 (49.5%) males, 90 patients (26.4%) were under 60 years of age, and 250 (73.6%) were over 60 years of age. Alzheimer's disease, with 89 cases (26%), followed by vascular dementia with 39 cases (11.47%), were the leading etiological diagnoses. A total of 193 patients had dementia and 37 of these (19.17%) were found to have potentially reversible dementias, distributed as follows: head injury: 15 patients; alcohol-related dementias: 11 patients; meningoencephalitis: 2 patients; hypothyroidism: 2 patients; neurosyphilis: 2 patients; normal pressure hydrocephalus: 2 patients; AIDS: 1 patient; Korsakoff's syndrome: 1 patient, and Post-anoxic dementia: 1 patient. A significant number of patients were found to have potentially reversible dementias (19.17%). These data show an urgent need for more extensive diagnostic investigation, and indicate the possibility of reversing some dementias, especially cases detected early.