Although pneumonia is the hallmark of Mycoplasma pneumoniae infections, it has been associated with protean manifestations such as extrapulmonary involvement. Herein, a rare case of mononuclear syndrome with acute hepatitis and erythema multiforme revealed as M pneumoniae infection without lung involvement is reported. A 30-year-old man, previously healthy, presented with fever and rash with acute hepatitis: AST 603 IU/L, ALT 747 IU/L, prothrombin time 52%. Peripheral blood smears indicated monocytosis with atypical lymphocyte. Bone marrow biopsy revealed increased plasma cell infiltration. M pneumoniae infection was detected by serology testing. After treatment with macrolide, clinical symptoms and signs and serological tests were fully resolved. Diagnosis of this etiologic association is important when patients present with various clinical syndromes without pneumonia, because only specific antimicrobial therapy is effective against M pneumoniae.