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PURPOSE Whether preexisting sleep disorder is an independent risk factor for cancer remains unclear. Therefore, we performed this propensity score-matched population-based cohort study to compare the incidence rate ratios (IRRs) of specific cancers between patients with and without sleep disorders. PATIENTS AND METHODS Patients were categorized into two groups on the basis of the presence or absence of sleep disorders and matched at a 1:1 ratio. RESULTS Propensity score matching yielded a final cohort of 289,162 patients (i.e., 144,581 and 144,581 in the sleep disorder and nonsleep disorder groups, respectively) who were eligible for further analysis. In multivariate Cox regression analysis, the adjusted hazard ratio (aHR; 95% confidence interval [CI]) of cancer risk in the sleep disorder group compared with the nonsleep disorder group was 1.07 (1.04-1.12; P = 0.0001). Furthermore, the adjusted IRRs (95% CIs) for all cancers, breast cancer, and ovarian cancer in the patients with sleep disorders were 1.08 (1.02-1.18), 1.20 (1.08-1.32), and 1.30 (1.10-1.52), respectively. CONCLUSION The results suggested that sleep disorders are a significant risk factor for all cancers, breast cancer, and ovarian cancer.