The reason for undertaking this study was that postoperative complications of colic surgery lead to patient discomfort, prolonged hospitalisation and increased cost. Potential risk factors for the 6 most common postoperative complications (jugular thrombosis, ileus, re-laparotomy, wound suppuration, incisional herniation and colic) were evaluated using multivariable models. Jugular thrombosis was associated significantly with heart rate greater than 60 beats/min and with increased packed cell volume (PCV) at admission. The risk of postoperative ileus also increased with increasing PCV at admission and was higher in horses recovering from pedunculated lipoma obstruction. Incisional herniation was strongly associated with wound suppuration and with increasing heart rate at admission. The emergence of cardiovascular parameters as risk factors for several postoperative complications is consistent with the hypothesis that endotoxaemia is important in the development of these complications. Early referral of colic cases, prior to the development of severe endotoxaemic shock, may minimise the risk of some postoperative complications. Horses that have suffered epiploic foramen entrapment, are more than 4 times as likely to undergo re-laparotomy than other horses. Horses that have suffered postoperative ileus have a similarly increased risk of undergoing re-laparotomy. The risk of postoperative colic is significantly associated with horses recovering from large colon torsion (>360 degrees) and with having undergone re-laparotomy. Hazard ratios (with 95% confidence intervals) for these last two effects are 3.1 (1.7, 5.7) and 3.4 (1.9, 6.2), respectively. Knowledge of the risk factors for postoperative complications allows more accurate prognostication postoperatively and suggests ways in which the risk of postoperative complications can be minimised.