Dementia is a major public health problem among the very old. Available information on incidence and prevalence is sparse and variable; however, there appears to be a higher prevalence among very old women. We present data from a prospective study of initially nondemented community-residing elderly. There were 75 incident dementia cases (up to 7 years of follow-up) of which at least 47% were probable Alzheimer's disease. Based on a proportional hazards analysis, women were over 3 times more likely to develop dementia than men despite controlling for baseline demographic, psychosocial, and medical history variables. Poor word fluency and a high normal Blessed test score at baseline were also strong predictors of dementia. We did not find age, head trauma, thyroid disease, or family history of dementia to be risk factors. A new finding is that history of myocardial infarction (MI) is associated with dementia, such that women with a history of MI were 5 times more prone to dementia than those without a history. This observation was not true for men.