We report a streptozotocin-induced diabetic cynomolgus monkey that developed acute gastric dilatation within the first week after intraportal porcine islet transplantation. The monkey presented with increasing anorexia and somnolence, associated with persistent metabolic acidosis. On physical examination, a diffuse mass was palpable in the abdomen. Because of its deteriorating clinical condition, the monkey was euthanized. Necropsy revealed acute gastric dilatation. Potential etiological factors, possible methods of prevention, and guidelines for management are reviewed, with special emphasis on the incidence and management of acute gastric dilatation in non-human primates.