BACKGROUND: Postoperative cognitive dysfunction (POCD) is a typical consequence following surgery, particularly in cardiac surgeries. Despite its high incidence, the underlying etiology remains unclear. While diabetes mellitus (DM) has been associated with cognitive impairment, its specific function in POCD development remains unidentified. This study aims to evaluate the connection between DM and the risk of POCD. METHODS: We conducted a comprehensive search of PubMed, Embase, Web of Science, and the Cochrane Library databases for studies of DM and risk with POCD, collecting data up to 14 September 2023. We assessed publication bias, heterogeneity, and study quality, adhering to PRISMA and AMSTAR guidelines. RESULTS: Our study comprised 38 trials involving 8748 individuals, with 7734 patients undergoing follow-up. The pooled results showed that individuals with DM had an increased incidence of POCD compared to nondiabetic individuals (RR: 1.44, 95% CI: 1.26-1.65). The incidence of POCD was significantly higher in the group of patients with an average age older than 65 years (RR: 1.69, 95% CI: 1.30-2.20) compared with diabetic patients with an average age younger than 65 years (RR: 1.29, 95% CI: 1.09-1.64). Compared with diabetic patients undergoing cardiac surgery (RR: 1.33, 95% CI: 1.15-1.53), patients receiving non-cardiac surgery showed a greater incidence of POCD (RR: 2.01, 95% CI: 1.43-2.84). CONCLUSION: Current evidence underscores that diabetic patients face a significantly higher risk of POCD compared to their nondiabetic counterparts. Further research is warranted to clarify the precise mechanisms of this relationship and explore potential preventive strategies for diabetic patients.