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Objective: Bronchial asthma and obstructive sleep apnoea (OSA) are common respiratory disorders that can co-exist. The strength of this association, and also the impact of OSA on asthma-related clinical outcomes remain unclear. Data Sources: Literature review was performed in EMBASE and MEDLINE databases. Studies up to and including 2016 were selected. Study Selection: Studies were included if they contained; 1) a population with asthma AND 2) a prevalence of OSA reported using either polysomnography or validated questionnaires such as the Sleep Apnoea Scale of the Sleep Disorders Questionnaire (SA-SDQ), STOP BANG or the Berlin questionnaire. Results: Nineteen studies were identified. Thirteen questionnaire-based studies met the inclusion/exclusion criteria and twelve of these demonstrated a prevalence of OSA in asthma of 8-52.6%, with one study showing no association between the two conditions. Six studies using polysomnography demonstrated a high prevalence of 19.2-60%; which was higher at 50-95% in severe asthma. Two polysomnography and four questionnaire studies found worse asthma-related clinical outcomes with co-existing OSA. One polysomnography and two questionnaire studies showed no difference. Conclusion: This systematic review suggests that there is a high prevalence of OSA in asthma, particularly within severe asthma populations and that co-diagnosis of OSA in asthma patients is associated with worse clinical outcomes. However this outcome was not uniform and the number of studies using polysomnography to confirm OSA was small. This weakens the conclusions that can be drawn and prompts the need for adequately powered and well-designed studies to confirm or refute these findings. [ABSTRACT FROM AUTHOR]