An 11-year-old boy with a high fever (39.4°C) presented at a local medical institution. His condition was diagnosed as hemolytic streptococcal infection, and he was prescribed an antibiotic. After returning home, he took a dose of his medication and rested; however, he suddenly began to run around while yelling incomprehensible words. He ran up to his room on the second floor and fell from the second floor window down to the ground. He lost consciousness and was transferred to our department. His history included being born as a twin with a low birth weight and pneumonia at 1 year of age. He regained consciousness on the seventh hospital day and was discharged without any neurological abnormality on the 14th day. His abnormal behavior might have resulted from febrile delirium or an unusual expression of pediatric autoimmune neuropsychiatric disorder associated with a streptococcal infection.