BACKGROUND: The aim of this study was to identify risk factors in emergency surgery for colonic cancer in a large population and to investigate the economic impact of such surgery. METHODS: Data from the colonic cancer registry (1997-2001) of the Uppsala/Orebro Regional Oncological Centre were analysed and classified by hospital category. Some 3259 patients were included; 806 had an emergency and 2453 an elective procedure. Data for calculating effects on health economy were derived from a national case-costing register. RESULTS: Patients who had emergency surgery had more advanced tumours and a lower survival rate than those who had an elective procedure (5-year survival rate 29.8 versus 52.4 per cent; P