Gastroesophageal intussusception is a rare condition in dogs. We report a gastroesophageal intussusception in an adult dog which had been subjected to unilateral pneumonectomy as a pup. One year after the surgery, computerized tomography scans indicated megaesophagus in the caudal third of the thorax. However, clinically the dog had experienced only a few episodes of vomiting of bile-stained fluid, which was not associated with eating. At 15 months after surgery, the dog was found dead without prior clinical signs of disease. At that time, gastroesophageal intussusception was identified. The cause of the intussusception is not known, although megaesophagus may be a predisposing factor.