Purpose: Emergency abdominal surgery results in a high rate of post-operative complications and death. There are limited data describing the emergency surgical population in details. We aimed to give a detailed analyses of complications and mortality in a consecutive group of patients undergoing acute abdominal surgery over a 4-year period. Methods: This observational study was conducted between 2009 and 2013 at Copenhagen University Hospital Herlev, Denmark. All patients scheduled for emergency laparotomy or laparoscopy were included. Pre-, intra-, and post-operative data were collected from medical records. Complications were registered according to the Clavien-Dindo classification. Cox regression analysis was performed to identify risk factors for mortality. Results: A total of 4,346 patients underwent emergency surgery, of whom 14 % had surgical complications and 23 % medical complications. The overall 30-day mortality was 8 % with 50 % of those in this group over 80 years of age. The 30-day mortality rates were 0.8 % (95 % CI 0.5–1.1) and 17 % (95 % CI 15.5–18.9), respectively, for the laparoscopy and the laparotomy groups. The overall death rate within 24 h of surgery was 21 %. Several risk factors for 30- and 90-day mortality were identified: age, ASA ≥3 (American Society of Anaesthesiologists physical status classification), performance score (Zubroed/WHOclassification), cirrhosis of the liver, chronic nephropathy, several medical conditions, and malignancy. Conclusion: Almost one in five patients died after emergency laparotomy, of whom one in five died within 24 h of surgery. Predictors for poor outcome were identified.