Mycoplasma pneumoniae is a common cause of respiratory tract infection. Extrapulmonary manifestations of M. pneumoniae infection are also common. The present case is that of a previously healthy 4-year-old boy who displayed a novel simultaneous onset of both acute rhabdomyolysis and transverse myelitis associated with an infection of M. pneumoniae. He had no preceding symptoms or signs of respiratory tract infection. Intravenous immunoglobulin (1 g/kg per day) for 2 days was prescribed initially for the deterioration of neurologic condition. His rhabdomyolysis resolved without complication, but neurologic sequelae remained during 2 years of follow-up. Evaluation for M. pneumoniae infection is recommended in patients with idiopathic rhabdomyolysis and transverse myelitis, even if in the absence of antecedent respiratory symptoms.