Gastroscopy is the most common technique used in veterinary medicine to evaluate the stomach in horses and to date, no complications have been described associated with the procedure. This paper reports 4 cases developing a nonstrangulating segmental volvulus of the small intestine after gastroscopy at 3 referral institutions over a 2 year period. After performing diagnostic gastroscopy, all horses developed acute and severe clinical signs of colic unresponsive to medical management. Time range between gastroscopy and onset of colic signs varied from 10 min to 3 h. An exploratory laparotomy revealed a nonstrangulating segmental volvulus of the small intestine that was manually corrected without need for resection in all horses. In all cases, affected small intestine was severely gas distended. Three of those horses survived to discharge and were alive at follow-up. One horse was subjected to euthanasia 2 days after surgery due to diffuse intestinal lymphoma.