Cognitive impairment affects nearly half of vascular surgery patients, but its association with postoperative outcomes remains poorly understood. This study explores the link between preoperative cognitive performance and postoperative complications, including postoperative delirium, in vascular surgery patients. A prospective cohort study was conducted on vascular surgery patients aged ≥65. Preoperative cognitive performance was assessed using the Montreal Cognitive Assessment, and postoperative complications were evaluated using the Comprehensive Complication Index. The association was analyzed through multivariable logistic regression. Among 110 patients (18.2 ​% female, mean age 73.8 ​± ​5.7 years), cognitive impairment was evident in 48.2 ​%. Of the participants, 29 (26.3 ​%) experienced postoperative complications, among which 11 (10 ​%) experienced postoperative delirium. The adjusted odds ratio for the association between cognitive performance and postoperative complications was 1.19 (95 ​% CI 1.02–1.38; p ​= ​0.02). Worse preoperative cognitive performance correlated with increased odds of postoperative complications and postoperative delirium in vascular surgery patients. •Approximately 50 ​% of vascular surgery patients exhibit cognitive impairment.•Worse preoperative cognitive performance was associated with increased odds of postoperative complications and delirium among vascular surgery patients.•Postoperative cognitive decline was significantly linked to lower baseline educational levels and a history of cerebrovascular disease.•More focus is needed on strategies to minimize complications in individuals with preexisting cognitive impairment.