Background Postoperative delirium (POD) is a serious complication in patients undergoing microvascular head and neck reconstruction. Whether intraoperative and postoperative blood pressure regulation are risk factors for POD remains unclear. This study aimed to highlight the relationships between intraoperative and postoperative blood pressure regulation and POD in microvascular head and neck reconstruction. Methods Data from 433 patients who underwent microvascular head and neck reconstruction at our department of oral and maxillofacial surgery between 2011 and 2019 were retrospectively analyzed. The 55 patients with POD were matched with 55 patients without POD in terms of tracheotomy, flap type, and flap location, and the intraoperative and postoperative systolic and mean blood pressure values were compared between the two groups. Results Patients with POD showed lower intraoperative and postoperative minimum mean arterial pressure (MAP) values than patients without POD (60.0 mmHg vs. 65.0 mmHg, p < 0.001; and 56.0 mmHg vs. 62.0 mmHg, p < 0.001; respectively). A lower intraoperative minimum MAP value was identified as predictor for POD (odds ratio OR 1.246, 95% confidence interval CI 1.057-1.472, p = 0.009). The cut-off value for intraoperative MAP for predicting POD was less than or equal to 62.5 mmHg (area under the curve AUC 0.822, 95% CI 0.744-0.900, p < 0.001). Conclusions Maintaining a stable intraoperative minimum MAP of > 62.5 mmHg could help to reduce the incidence of POD in microvascular head and neck reconstruction. Keywords: Postoperative delirium, Microvascular free flap, Head and neck reconstruction, Risk factor, Blood pressure regulation