BACKGROUND Mucosal erosions in bullous diseases and leading to mucosal sequelae are widely described in toxic epidermal necrolysis (TEN). These complications cause disfigurement and functional impairment. They are more rarely reported in erythema multiforme (EM). We report a case of lip adhesion following EM induced by Mycoplasma pneumoniae. METHODS A 12-year-old boy was hospitalized in a paediatric intensive care unit. He had a prominent target skin rash on the palms and soles. Mucosal injury was associated with conjunctivitis, balanitis without dysuria and hyperalgesic stomatitis. M. pneumoniae serology was positive with immunoglobulin M. We made a diagnosis of EM secondary to M. pneumoniae infection. Two months later, the skin lesions had completely disappeared but the patient's mouth opening was limited to 25 mm and he presented bilateral adhesions between the upper and lower lips of 5mm on the right and 8mm on the left resulting in aesthetic and functional damage. CONCLUSIONS Mucosal damage and its sequelae have been widely described in TEN. Ophthalmic sequelae are more frequent. A case of labial synechiae secondary to TEN has been reported. In EM, mucosal lesions occur in 100% of cases with a further mucosal problem being present in 50% of patients. Mucosal damage has been reported during EM flares but there are no studies of side-effects after the acute episode. Oral mucosal adhesions can cause cosmetic sequelae, but above all they hinder functional prognosis. These complications must be prevented by making gutters of vestibular deepening and lip movements with maximum mouth opening several times a day, starting as soon as possible. Appropriate pain management should be undertaken to ensure patient comfort and avoid the need for analgesics and restriction of movement. CONCLUSIONS Mucosal sequelae exist in EM. Whatever their cause, complications involving the mucosa must be prevented through early, tailored and multidisciplinary treatment. Adequate pain management must not be overlooked.