The aim of this study was to explore whether there is a relationship between cataract and Alzheimer's disease in older people in Taiwan. We conducted a retrospective cohort study by using the database of the Taiwan National Health Insurance Program from 1999 to 2004. There were 19,954 subjects aged 65-84 with newly diagnosed cataract as the cataract group and 19,954 randomly selected subjects without cataract as the non-cataract group. Both groups were matched with sex, age and index year of diagnosing cataract. The risk of Alzheimer's disease associated with cataract was assessed. The overall incidence of Alzheimer's disease was 1.21 per 1,000 person-years in the cataract group and 0.73 per 1,000 person-years in the non-cataract group (crude hazard ratio 1.62, 95 % CI 1.28, 2.04). After adjustment for potential confounders, the adjusted HR of Alzheimer's disease was 1.43 (95 % CI 1.13, 1.82) for the cataract group, compared to the non-cataract group. Male (HR 1.36, 95 % CI 1.09, 1.70), age (every 1 year, HR 1.08, 95 % CI 1.06, 1.10) and head injury (HR 1.79, 95 % CI 1.08, 2.96) were other factors significantly associated with Alzheimer's disease. Older people with cataract are at 1.43-fold increased risk of developing Alzheimer's disease. More research is necessary to determine whether cataract is one of non-memory features of Alzheimer's disease.