Background: Erythema multiforme (EM) is an acute immune-mediated mucocutaneous disorder characterized by targetoid skin lesions and variable mucosal involvement. Infections account for the majority of cases, with herpes simplex virus being the most common trigger. Mycoplasma pneumoniae is another important infectious cause, particularly in children and adolescents, where it may present with prominent mucosal involvement.

Case Presentation: A 14-year-old female presented with fever, cough, throat pain, wheezing, and progressive swelling of the lips associated with painful blisters. She had received oral paracetamol and amoxicillin-clavulanic acid prior to presentation. On examination, she was tachycardic, mildly tachypneic, hypoxemic, and had bilateral rhonchi with significant lip edema and vesiculobullous lesions involving the oral mucosa. Chest radiography revealed features suggestive of bronchopneumonia. Dermatological evaluation confirmed erythema multiforme secondary to underlying respiratory infection, most likely Mycoplasma pneumoniae-associated. The patient was treated with oxygen supplementation, bronchodilators, corticosteroids, antihistamines, macrolide antibiotics, and supportive local care. Significant clinical improvement was observed, and she was discharged after five days.