The link between psoriasis and obstructive sleep apnea (OSA) has not been confirmed. We aimed to investigate the relationship between psoriasis and OSA. We conducted a systematic review and metaanalysis of case-control, cross-sectional, and cohort studies on the association between psoriasis and OSA. We searched MEDLINE and Embase for relevant studies on May 11, 2019. The Newcastle-Ottawa Scale was used to evaluate the risk of bias of included studies. We performed random-effects model meta-analysis to calculate pooled odds ratio (ORs) with 95% confidence intervals (CIs) for case-control and cross-sectional studies as well as pooled incidence rate ratio (IRR) with 95% CIs for cohort studies in association between psoriasis and OSA. A total of 4 case-control or cross-sectional studies and 3 cohort studies with a total of 5,840,495 subjects were included. We identified a significantly increased odds for OSA in psoriasis patients (pooled OR 2.60; 95% CI 1.07-6.32), and significantly increased risk for psoriasis in OSA patients (pooled IRR 2.52; 95% CI 1.89-3.36). In conclusion, our study identified a bidirectional association between psoriasis and OSA. Sleep quality should be inquired in patients with psoriasis. Respirologist consultation or polysomnography may be indicated for those presenting with night snoring, recurrent awaking, and excessive daytime sleepiness. Psoriasis is a chronic inflammatory skin disease with characteristic feature of sharply circumscribed erythematous plaques with silvery scales on the trunk and limbs 1. The prevalence was estimated 0.5-11.4% in adults 2. Psoriasis is considered as a multisystemic disease involving proinflammatory cytokines such as tumor necrosis factor (TNF), interleukin (IL)-1, and IL-17 3,4. Various comorbidities have been linked to psoriasis including cardiovascular disease, metabolic syndrome, chronic kidney disease, uveitis, thyroid diseases, vitiligo, and inflammatory bowel disease 5-11. Obstructive sleep apnea (OSA), also called obstructive sleep apnea-hypopnea syndrome, is a chronic disorder of intermittent upper airway collapse during sleep resulting in recurrent hypoxia 12,13. OSA is characterized with night snoring, recurrent awaking, and excessive daytime sleepiness 14. The gold standard test for diagnosing OSA is polysomnography 15. The prevalence of OSA ranges from 3 to 17% 12. Risk factors of OSA include obesity, aging, male gender, anatomical predisposition, and alcohol consumption 12,13. OSA induces systemic inflammatory and increases the risk of hypertension, stroke, cardiovascular disease, and metabolic disorder, in particular of diabetes mellitus type 2 and metabolic syndrome regardless of the obesity 15-17. Psoriasis and OSA share a common pathogenesis of inflammatory and immune imbalance 18,19. The association between psoriasis and OSA has been examined in many studies but the results were limited and inconsistent 20-27. The objective of this study was to assess the evidence regarding the bidirectional association between psoriasis and OSA. Methods ...