ObjectiveTo assess the risk of Alzheimer's disease (AD) in patients with obstructive sleep apnea (OSA) with or without treatment based on real‐world evidence.Study DesignRetrospective cohort study.MethodsPatients newly diagnosed with OSA during 1997–2012 were identified using the National Health Insurance Research Database of Taiwan. Patients without OSA were randomly selected and matched in a 1:4 ratio by age, sex, urbanization level, and income. All patients were followed up until death or the end of 2013. The primary outcome was AD occurrence.ResultsThis study included 3,978 OSA patients and 15,912 non‐OSA patients. OSA was independently and significantly associated with a higher incidence of AD in an adjusted Cox proportional hazard model (adjusted hazard ratio: 2.12; 95% confidence interval [CI], 1.27–3.56). The average period of AD detection from the time of OSA occurrence was 5.44 years (standard deviation: 2.96). Subgroup analyses revealed that the effect of OSA remained significant in patients aged ≥60 years, male subgroups, patients without CPAP or surgical treatment, and patients without pharmacological therapies. Patients with OSA who received treatment (continuous positive airway pressure or surgery) exhibited a significantly reduced risk of AD compared with those without treatment (incidence rate ratio 0.23, 95% CI, 0.06–0.98).ConclusionOSA is independently associated with an increased risk of AD. Treatment for OSA reduces the AD risk in OSA patients. AD irreversibility renders OSA as a potential modifiable target for slowing or preventing the process of AD development.Level of EvidenceIV Laryngoscope, 130:2292–2298, 2020