Recurrent aphthous stomatitis is the most common oral mucosal disease in North America but it is commonly misdiagnosed and poorly understood. Pediatricians, internists, otolaryngologists, oral surgeons, and dentists may all be expected to treat this illness but little formal training in oral medicine may be offered to many of these health care professionals. This article reviews current evidence regarding etiology, pathogenesis, natural history, and treatment of this disorder.