Mycoplasma pneumoniae-associated mucositis is a rarely described complication of M. pneumoniae infection presenting with ocular, oral, and genital involvement but without the typical skin lesions seen in Stevens-Johnson syndrome. A 27-year-old man with a past history of asthma presented at the emergency room with a 1-week history of cough (initially non-productive but subsequently associated with non-bloody mucopurulent sputum), fever, myalgias, headache, and progressive dyspnea. Two days before admission he had commenced amoxicillin/clavulanic acid with no improvement. The patient reported bilateral conjunctival injection and hemorrhagic ulcers on the lips commencing the day prior to admission. Physical examination revealed fever (39 degrees C), bilateral exudative conjunctivitis, painful hemorrhagic ulcers on the lips, tongue, and oral mucosa, small scrotal erosions, erythema of the penile meatus, and small erythematous bullae on the dorsum of each hand; subsequently, the patient developed bullae at the venipuncture site on his right arm. Laboratory tests revealed positive IgM serology for M. pneumoniae, with titer elevation. The patient was successfully treated with levofloxacin and prednisolone. Our case appears to be the first adult patient described with M. pneumoniae-associated mucositis, which has previously been reported only in pediatric patients. This is also the first reported instance of a case of M. pneumoniae-associated mucositis treated with levofloxacin and prednisolone. M. pneumoniae infection should be considered in all cases of mucositis, and treatment of this condition with levofloxacin and prednisolone seems to be effective.