Although intraoral involvement in Crohn's disease (CD) is observed in only approximately 9% of cases, oral inflammation precedes intestinal symptoms of CD in about 60% of these patients. We describe a 20-year-old male with recurrent, painful, intraoral lesions who presented no other signs of systemic disease apart from severe loss of body weight. From the routinely screened serological parameters only the erythrocyte sedimentation rate and the acute phase reactants were elevated. A biopsy from the vestibular mucosa revealed a dense mononuclear infiltrate and, focally, small noncaseating granulomas suggestive of CD. Gastrointestinal endoscopy was performed showing mucosal involvement reaching from the esophagus to the descending colon. The diagnosis of active CD was confirmed by histopathology of intestinal biopsy specimens. As oral lesions are sometimes treated without a definite diagnosis, we emphasize the need to search for underlying systemic illness in the differential diagnosis of recurrent inflammatory lesions of the oral cavity.