Abstract We present a case of omental pseudocyst associated with a perforated gastric duplication. A boy (2.5 years old) with an abdominal mass was admitted because thick-walled and thin-walled double cysts were identified on computed tomography and magnetic resonance imaging. At laparotomy, the double cysts were interconnected and located in the omentum with no communication to the stomach. Microscopic examination showed a thick-walled cyst composed solely of gastric tissue with muscle layers divided at the stricture between the 2 cysts and a thin-walled cyst without a true endothelial lining. Gastric duplications can be complicated with perforation and malignancy, and primary surgery is the first choice of treatment.