We report a case of gastric heterotopia in the gallbladder of an 18-year-old man. Symptoms of acute cholecystitis are characteristic in patients under 20 years old, while older patients present with chronic cholecystitis and gallstones. The heterotopic mucosa results either in a mass, a polyp, or a multiloculated gallbladder. Twenty-eight other cases of gastric heterotopia in the gallbladder or cystic duct have been reported. In only three was it associated with peptic ulceration. Treatment is cholecystectomy. Heterotopic gastric mucosa has been described throughout the length of the gastrointestinal tract from the oral cavity to the rectum. Curiously, it is extremely rare in the gallbladder, where it has the propensity for causing symptoms of acute cholecystitis, particularly in the young. We report a case of this condition in which there was a separate loculus lined by gastric epithelium.