BACKGROUND: The relationship between cigarette smoking and development of Alzheimer's disease (AD) is not fully determined, and previous reports disagree, with some studies suggesting an increased relative risk and others a decreased odds ratio. Consequently, we wanted to determine if the prevalence of past cigarette smoking observed in a community-based clinic sample of patients with AD would be more consistent with the expected value obtained from a model using either an increased relative risk or a decreased odds ratio to estimate the effect of smoking on development of AD. MATERIALS AND METHODS: Retrospective cross-sectional analysis of all patients treated for AD in a community-based Neurology Clinic during a 2-year period. Estimates of expected past smoking prevalence were calculated based on published values for either an increased relative risk or a decreased odds ratio and compared to the past smoking prevalence observed in the clinic sample. RESULTS: The observed past smoking prevalence in the clinic population was 29.17%. The expected past smoking prevalence calculated using the increased relative risk was 30.07% (95% confidence interval [CI] = 27.67-32.32%), and using the decreased odds ratio was 12.54% (95% CI = 6.32-24.81%). CONCLUSION: The observed past smoking prevalence among the patients being treated for AD in a community-based clinic falls within the expected 95% CI for the increased relative risk model and outside of the expected 95% CI for the decreased odds ratio model. These results support the contention that the relationship between cigarette smoking and development of AD is the best characterized by an increased relative risk.