Dentistry is a branch of medicine that focuses on the health status of the oral cavity, it also strongly integrates with other areas of medicine, as the health of the oral cavity may influence the health condition of other organs of the body. The gastrointestinal system, in particular, can be influenced by the oral cavity, as the oral cavity serves as an initial entrance to the gastrointestinal tract. Oral and gastrointestinal diseases can affect each other. The major role of the oral cavity is biting, chewing and mixing of food particles with saliva to form ‘bolus’ ready for swallowing and passing through the pharynx and the esophagus to the stomach. Dentists and gastroenterologists anticipated to recognize and diagnose oral and gastric conditions associated with gastrointestinal system beginning from the oral cavity. The aim of the current review is to describe the oral manifestations of gastrointestinal (GI) diseases which are important in the screening of GI disorders which may otherwise be undiagnosed. The review includes peptic ulcer diseases, gastroesophageal reflux disease, coeliac disease, Inflammatory bowel diseases and syndromes affecting both the GI system and oral cavity.