Congenital idiopathic megaesophagus is an inherited gastrointestinal disease in dogs. In dogs with this condition, the normal movement of ingested food or water to the stomach is impaired resulting in an enlarged esophagus. Affected dogs regurgitate meals and water, suffer development deficiencies due to malnutrition, and can experience complications such as aspiration pneumonia. Signs are observed typically at 4 weeks of age coinciding with weaning. Many affected pups are euthanized due to complications, but some may survive with intensive life-long management. Among surviving dogs, a small percentage may spontaneously resolve by one year of age. Studies indicate males are more likely to develop clinical signs than females, but the precise cause of this sex predilection is uncertain.