Introduction: An individual classified as American Society of Anesthesiologists (ASA) physical status 5 (ASA 5) is described as “a moribund patient who is not expected to survive without the operation.” We examined the outcomes of ASA 5 patients who underwent an index neurosurgical operation to characterize surgical results and to identify risk factors for adverse outcomes in this population. Methods: We used the American College of Surgeons National Surgical Quality Improvement Program (NSQIP) database to identify 689 ASA 5 patients who underwent neurological surgery at any one of the 706 institutions participating in the NSQIP between 2006 and 2016. We used univariate logistic regression to identify baseline factors associated with adverse post-operative outcomes; all factors identified were incorporated into the final multivariate models. Results: Of the entire study population of 689 patients, 90% (n = 620) had an emergency operation and 89% (n = 613) had a cranial procedure. At 30 days, 11% remained hospitalized, 5% had been readmitted to an acute care hospital, 16% required an additional, unplanned surgery, and 39% had expired. The most common post-operative complications were prolonged (>48 h) mechanical ventilation (57%), transfusion of blood or blood products (26%), and pneumonia (23%); for patients with these complications, the 30-day mortality rates were 61%, 33%, and 19%, respectively. The vast majority (81%) of those who survived to discharge required continued care at a location other than home.In multivariate models, a variety of medical, surgical and socioeconomic factors were identified that increased the risk of prolonged length of stay, peri- and post-operative transfusion of blood or blood products, unplanned return to the operating room, re-admission within 30 days, and continued care after discharge. Conclusions: While post-operative complications are common, >60% of ASA 5 patients who undergo neurosurgery survive and 20% are discharged home within 30 days. These novel findings may be useful to inform decision-making in critically-ill neurosurgical patients. Keywords: Surgery, Mortality, Length of stay, Complications, Risk factors, Health services research, Neurosurgery, Craniotomy, Re-admissions, Re-operation, Brain, Spine