Abstract A seven-year-old Thoroughbred racing stallion was evaluated at the Cornell University Equine Hospital Emergency Service for chronic, intermittent colic of increasing severity of four years duration. At presentation, the patient was dehydrated, and had mild hypoproteinemia and hypoalbuminemia. The stomach was significantly distended, and 8L of reflux was obtained with nasogastric tubing, indicating an obstructive process. Ultrasound revealed diffusely thickened small intestines up to 2.1cm thick characterized by a moderate to severely thickened muscularis layer. Biopsy of the duodenum and rectum revealed mild microscopic changes that would be expected to be subclinical. A presumptive diagnosis of idiopathic muscular hypertrophy was made based on ultrasonographic evidence, and the stallion was started on a complete pelleted diet to minimize the potential for future obstruction. Idiopathic muscular hypertrophy has only rarely been reported in equines, and a potential association with inflammatory bowel disease in this patient is proposed.