Oral diverticulum is rarely encountered, and the histopathological findings are unclear. We herein report a case of an oral diverticulum and describe its histopathological findings. A buccal mucosal outpouching was observed in a 66-year-old man. Food debris was seen within the outpouching. Under the clinical diagnosis of a diverticulum-like lesion, excision of the outpouching was performed through an intraoral incision to stop food impaction. Histopathological examination revealed that the excised lesion was a true diverticular structure composed of a keratinising, squamous epithelial lining with a surrounding fibrous connective tissue wall, with inflammatory cell infiltration and haemorrhage. The histopathological diagnosis was a diverticular pouch of the buccal region. Clinicians should be aware of this lesion to ensure correct diagnosis and treatment.