PURPOSE: The association of diabetes mellitus with knee stiffness after total knee arthroplasty is still being debated. The aim of this study was to assess through meta-analysis the impact of diabetes mellitus on the prevalence of postoperative knee stiffness after total knee arthroplasty. METHODS: We conducted a literature search for terms regarding postoperative knee stiffness and diabetes mellitus on Embase, CINAHL, and PubMed NCBI. RESULTS: Of 1142 articles, seven were suitable for analysis. Meta-analysis showed that diabetes mellitus does not confer an increased risk of primary or revision total knee arthroplasty-induced postoperative knee stiffness when compared to nondiabetic patients (primary total knee arthroplasty, estimated odds ratio [OR] 1.474 and 95% confidence interval [CI] 0.97–2.23; primary and revision total knee arthroplasty, OR 1.340 and 95% CI 0.97–1.83). CONCLUSION There is no strong evidence that diabetes mellitus increases the risk of knee stiffness after total knee arthroplasty. The decision to proceed with total knee arthroplasty, discussion as part of the consent process, and subsequent rehabilitation should not differ between patients with and without diabetes mellitus with regards to risk of stiffness.LEVEL OF EVIDENCE: Level III (meta-analysis)