Heterotopic gastrointestinal cyst (HGIC), also referred to as gastric cystic choristoma, is extremely rare in the oral cavity. We report a case of a gastrointestinal cyst in the oral floor of a 3-month-old boy. Viscous fluid, colorless and transparent, was aspirated, and marsupialization of the lesion was performed. The tissue was submitted for histopathologic evaluation. The cyst wall was lined by simple columnar epithelium resembling that of the gastric mucosa. Most gastrointestinal cysts arising in the oral cavity have occurred in the tongue and the floor of the mouth. The histogenesis of thisc yst is related to entrapment of undifferentiated, noncommitted endoderm within the oral cavity during the 4th-5th week of fetal life. The patient has had no evidence of recurrence for 4.5 years after marsupialization of the cyst.
