We investigated the conversion rate and the risk factors for conversion to dementia from questionable dementia in 124 ethnic Chinese subjects with questionable dementia at a memory clinic of a university hospital. They were evaluated annually based on cognitive testing, the clinical dementia rating scale, and a psychiatrist's interview for depression and anxiety. Apolipoprotein E genotyping was performed on 111 of these questionable dementia subjects. All subjects were evaluated at least twice during the follow-up period of 20.4 +/- 12.4 months. During that period, 42 questionable dementia subjects were diagnosed as having Alzheimer's disease, with an annual conversion rate to dementia of 19.9%. Compared with the 82 nonconverters, the 42 converters were significantly older, had lower cognitive, depression, and anxiety scores, and a higher frequency of the apolipoprotein E epsilon4 allele. Cox regression analysis revealed that the Alzheimer's disease converters had lower scores for orientation, short-term memory, and anxiety, and a higher frequency of the apolipoprotein E epsilon4 allele than the nonconverters.