Gastrointestinal stromal tumours (GISTs), previously termed leiomyomas and leiomyosarcomas are relatively common tumours of the gastrointestinal tract, most commonly found in the stomach. Most GISTs are asymptomatic but may cause abdominal pain or bleeding from ulceration of the overlying mucosa. A rare case of gastroduodenal intussusception of a large gastric stromal tumour, which presented with intermittent abdominal pain and gastric outlet obstruction, is reported. Pre-operative diagnosis was made on abdominal CT and confirmed at laparotomy. Pre-operative diagnostic difficulties and management are discussed.