Unrecognized obstructive sleep apnea (OSA) may lead to poor asthma control despite optimal therapy. Our objective was to evaluate the relationship between OSA risk and asthma control in adults. METHODS: Patients with asthma seen routinely at tertiary-care clinic visits completed the validated Sleep Apnea Scale of the Sleep Disorders Questionnaire (SA-SDQ) and Asthma Control Questionnaire (ACQ). An ACQ score of >or= 1.5 defined not-well-controlled asthma, and an SA-SDQ score of >or= 36 for men and >or= 32 for women defined high OSA risk. Logistic regression was used to model associations of high OSA risk with not-well-controlled asthma (ACQ full version and short versions). RESULTS: Among 472 subjects with asthma, the mean +/- SD ACQ (full version) score was 0.87 +/- 0.90, and 80 (17%) subjects were not well controlled. Mean SA-SDQ score was 27 +/- 7, and 109 (23%) subjects met the definition of high OSA risk. High OSA risk was associated, on average, with 2.87-times higher odds for not-well-controlled asthma (ACQ full version) (95% CI, 1.54-5.32; P = .0009) after adjusting for obesity and other factors known to worsen asthma control. Similar independent associations were seen when using the short ACQ versions. CONCLUSIONS: High OSA risk is significantly associated with not-well-controlled asthma independent of known asthma aggravators and regardless of the ACQ version used. Patients who have difficulty achieving adequate asthma control should be screened for OSA.