BACKGROUND: dementia risk conferred by apolipoprotein-E (APOE) and angiotensin-1-converting enzyme (ACE) polymorphisms have been reported for the MRC Cognitive Function and Ageing Study (CFAS) at 6-year follow-up. We concentrate on incident dementia risk over 10 years. METHODS: participants come from MRC CFAS, a multi-centre longitudinal population-based study of ageing in England and Wales. Three follow-up waves of data collection were used: 2, 6 and 10 years. Logistic regressions were undertaken to investigate associations between APOE (n = 955) and ACE (n = 856) alleles/genotypes and incident dementia. Two types of control groups were used: non-demented and highly functioning non-demented. Results were back-weighted. RESULTS: compared to APOE epsilon3, epsilon2 conferred protection of odds ratio (OR) = 0.3 (95% confidence interval, CI = 0.1-0.6) and epsilon4 risk of OR = 2.9 (95% CI = 1.7-4.9) for incident dementia. Compared to epsilon3/epsilon3, the epsilon3/epsilon4 and epsilon4/epsilon4 genotypes conferred risks of OR = 3.6 (95% CI = 1.8-7.3) and OR = 7.9 (95% CI = 1.6-39.2), respectively. The epsilon3/epsilon2 genotype protected against dementia (OR = 0.2, 95% CI = 0.1-0.7), and epsilon2/epsilon2 had a similar protective effect but with wide CIs (OR = 0.3, 95% CI = 0.1-1.7). Restricting the control group accentuated these differentials. The effects of ACE alleles/genotypes on incident dementia risk were small. CONCLUSIONS: APOE but not ACE is associated with late-onset incident dementia in the population. Using longer term follow-up with proper adjustment for attrition and incident cases increases estimates of risk.