Objective To retrospectively investigate the relationship between preoperative baseline cognitive function and postoperative delirium (POD) in Parkinson's disease (PD) patients undergoing deep brain stimulation (DBS) surgery. Methods Preoperative baseline data and PD‑related symptom scale scores, including the Non‑Motor Symptom Scale (NMSS) score, the Movement Disorder Society‑Unified Parkinson's Disease Rating Scale (MDS‑UPDRS) score, the KINGS Parkinson's Disease Pain Scale (KPPS) score, Hamilton Depression Scale (HAMD) score and Hamilton Anxiety Scale (HAMA) score were collected for retrospective analysis. The cognitive function of the patients was assessed by the Mini‑Mental State Examination (MMSE) score before surgery and 24, 72 h after surgery. Delirium was assessed by the Confusion Assessment Method (CAM) within 3 days after surgery. According to the presence of delirium after surgery, the patients were divided into two groups: a POD group and a non‑POD group. The relationship between preoperative cognitive function and POD was analyzed through binary logistic regression analysis. Results A total of 226 patients were included, where 37 patients (16.37%) presented POD. Compared with the non‑POD group, patients in the POD group showed increases in age, the incidence of diabetes, the operative time, as well as reduced MMSE scores before and 24 h and 72 h after surgery, increased NMSS scores, and increased scores in MDS‑UPDRS part Ⅰ, Part Ⅱ and Part Ⅲ (all P<0.05). There were no statistical differences in the number of female patients, body mass index (BMI), American Society of Anesthesiologists (ASA) grade, education level, the incidences of hypertension and coronary heart disease, NMSS score, KPPS score, HAMD score, HAMA score and MDS‑UPDRS Part Ⅳ score between the two groups (all P>0.05). Multivariate logistic regression analysis showed that preoperative MMSE score [odds ratio (OR) 0.83 (95% confidence interval (CI) 0.75, 0.93), P=0.001], age [OR 1.16 (95%CI 1.08, 1.26), P<0.001] and diabetes [OR 3.79 (95%CI 1.12, 12.81), P=0.032] were independently associated with POD. Conclusion Lower preoperative MMSE score, advanced age and diabetes are the independent risk factors for POD after DBS surgery in PD patients.