Guillain-Barré syndrome (GBS) and transverse myelitis may occur coexistently in the pediatric population. This may be explained by a shared epitope between peripheral and central nervous system myelin. Coexistent transverse myelitis, myositis, and acute motor neuropathy in childhood have not been previously described. We describe a 14-year-old female patient with transverse myelitis, myositis, and GBS following Mycoplasma pneumoniae infection. She presented with weakness and walking disability. Weakness progressed to involve all extremities and ultimately, she was unable to stand and sit. Based on the clinical findings, a presumptive diagnosis of myositis was made at an outside institution because of high serum creatine kinase level. The patient was referred to our institution for further investigation. Magnetic resonance imaging of spine revealed enhancing hyperintense lesions in the anterior cervicothoracic spinal cord. The electromyography revealed acute motor polyneuropathy. Serum M. pneumoniae IgM and IgG were positive indicating an acute infection. Repeated M. pneumoniae serology showed a significant increase in Mycoplasma IgG titer. The patient was given intravenous immunoglobulin for 2 days and clarithromycin for 2 weeks. She was able to walk without support after 2 weeks of hospitalization. This paper emphasizes the rarity of concomitant myositis, transverse myelitis, and GBS in children.