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Abstract Background The risk factors of postoperative delirium (POD), a serious while preventable complication, developed by patients undergoing knee and replacement surgery are still under investigation. In this systematic review and meta-analysis, we identified risk factors associated with POD in knee and hip replacement. Methods PubMed, Ovid MEDLINE, and Ovid EMBASE were used to identify original researches. The studies evaluating the risk factors of POD after knee and hip replacement were reviewed, and the qualities of the included studies were assessed with Newcastle–Ottawa Scale. Data were extracted, pooled, and a meta-analysis was completed Result Twenty-two studies were finally included with a total of 11934 patients who underwent knee or hip replacement and 1841 developed POD with an incidence of 17.6% (95% confidential interval (CI) 13.2–22.0%). Eighteen significant risk factors were identified including advanced age (odds ratio (OR) 1.15 95% CI 1.08–1.22), cognitive impairment (OR 6.84, 95% CI 3.27–14.33), history of cerebrovascular events (OR 2.51, 95% CI 1.28–4.91), knee replacement (OR 1.42, 95% CI 1.00–2.02), blood loss (standardized mean difference (SMD) 0.30, 95% CI 0.15–0.44), dementia (OR 3.09, 95% CI 2.10–4.56), neurologic disorders (OR 2.26, 95% CI 1.23–4.15), psychiatric illness (OR 2.74, 95% CI 1.34–5.62), and obstructive sleep apnea (OR 4.17, 95% CI 1.72–10.09) along with several comorbidity evaluation scores and laboratory markers. Conclusion We identified risk factors consistently associated with the incidence of POD in knee and hip replacement. Strategies and interventions should be implemented to the patients receiving knee or hip replacement with potential risk factors identified in this meta-analysis.