Purpose Delirium is a recognized complication of surgery. It has a deleterious effect on a patient’s postoperative recovery and well-being. The purpose of this study was to estimate the frequency and identify the risk factors for the development of postoperative delirium (POD) in a cohort of patients who underwent extensive head and neck surgery (HNS) of greater than five hours duration. Materials and Methods The authors undertook a retrospective cohort study of patients who underwent HNS of greater than five hours duration. The primary predictor variables comprised a set of risk factors (sociodemographic, disease-specific, duration of surgery, and duration of inpatient stay) that were thought to be associated with the development of POD. The primary outcome variable was the development of POD. Descriptive, bivariate, and multivariate statistical analysis was undertaken, and significance was set at P Results One hundred and seventy patients were included in the study. There were 124 males and 46 females. Forty patients (23.53%) developed POD: 30 documented and 10 inferred. The mean age of the POD cohort was 65 years (SD 13), with a median age of 69 years. The occurrence of POD was statistically related to increased age, mental health status, American Society of Anesthesiologists (ASA) score, and drug dependence (either illicit or prescription). POD and operative duration were statistically associated. POD and length of stay were not statistically associated. Conclusion Delirium did occur postoperatively in 23.53% of our patients who underwent extensive and prolonged HNS. POD may go unrecognized by treating teams. As POD has a deleterious effect on the cognitive function, it is important to identify and aggressively treat episodes of POD that occur during a patient’s postoperative recovery.