Objectives To determine the incidence of postoperative ileus (POI) in a population of horses after small intestinal surgery and the effect of multiple variables on development of POI. Study Design Case series. Animals Horses (n=233) aged ≥1 year that had exploratory celiotomy for small intestinal disease that recovered from surgery from 1995 to 2005. Methods Sixty-eight variables were collected from medical records (1995–2005) for each horse. POI was defined as nasogastric reflux volume >20 L over 24 hours or >8 L at any single time after surgery. Results Twenty-seven percent (64/233) of horses developed POI; 29 of 64 (46%) horses with POI had duodenitis proximal jejunitis (DPJ). When no intestinal resection was required at surgery, excluding horses with DPJ, 15% of horses had POI; 30% horses had POI after intestinal resection. Ten percent of horses had POI for >24 hours. When horses with DPJ were excluded, factors associated with increased risk of POI included high packed cell volume at hospital admission (P=.024), increasing age (P=.0004), and length of intestinal resection (P=.05). Conclusions Risk factors for POI in this study were nonspecific although horses with intestinal resection are at higher risk compared with horses without intestinal resection. Clinical Relevance Predicting with certainty which cases will develop POI remains elusive.