Crohn’s disease (CD) is a chronic inflammatory process with pathological changes which can involve any part of the gastrointestinal tract. Contrary to previous opinions, involvement of the oral cavity is frequent, but is rarely diagnosed. A thirty-years-old patient with deep ulceration of the oral mucosa which appeared during exacerbation of CD is presented. Granulomatous inflammation of the oral mucosa was confirmed by histopathology. Inflammatory changes typical for CD were present in the distal small bowel with ileo-ileal fistula and in the distal colon, and were confirmed by colonoscopy, histopathological examination of mucosal biopsies and double-contrast radiographic examination of the small bowel. Dental examination of a patient with active CD is helpful in the diagnosis of oral manifestations of the disease and mucosal biopsies can easily be taken for histopathological confirmation of granulomatous inflammation. In patients with CD the oral ulcerations are chronic and difficult to treat. The standard treatment of active CD plays the main role in the approach to these patients.