We experienced the case of a boy suffering from acute disseminated encephalomyelitis and concomitant acute glomerulonephritis. The multiple lesions observed on MR images, which located mainly in the cortical gray matter, quickly responded to methyl prednisolone pulse therapy. Renal biopsy confirmed the diagnosis of poststreptococcal acute glomerulonephritis. Streptococcus pyogenes was identified by pharyngeal culture, and the infection was serologically confirmed. We speculated that S. pyogenes infection was coincidentally involved in both diseases.