Aim Colon cancer resection in a nonelective setting is associated with high rates of morbidity and mortality. The aim of this retrospective study is to identify risk factors for overall mortality after colon cancer resection with a special focus on nonelective resection. Method Data were obtained from the Dutch Surgical Colorectal Audit. Patients undergoing colon cancer resection in the Netherlands between January 2009 and December 2013 were included. Patient, treatment and tumour factors were analysed in relation to the urgency of surgery. The primary outcome was 30-day postoperative mortality. Results The study included 30 907 patients. A nonelective colon cancer resection was performed in 5934 (19.2%) patients. There was a 4.4% overall mortality rate, with significantly more deaths after nonelective surgery (8.5% vs 3.4%, P < 0.001). Older patients, male patients and patients with high comorbidity, advanced tumours, perforated tumours, a tumour in the right or transverse colon and postoperative anastomotic leakage were at risk of postoperative death. In nonelective resections, a right-sided tumour and postoperative anastomotic leakage were associated with high mortality. Conclusion Nonelective colon cancer resection is associated with high mortality. In particular, right-sided resections and patients with tumour perforation are at particularly high risk. The optimization of patients prior to surgery and expeditious operation after diagnosis might prevent the need for a nonelective resection.@en