Human herpesvirus 7 (HHV-7) is ubiquitous and infects most children.���Severe HHV-7 infection was considered to be rare.���In this case series, we report the clinical findings and clinical courses of three immunocompetent children who had severe HHV-7 infection: two fatal cases of encephalopathy and one patient with severe sequelae after myocarditis.���In all three patients, HHV-7 DNA was detected in acute phase specimens, including serum by real-time PCR.���In the myocarditis case, HHV-7 DNA was also detected in myocardial tissue, suggesting that HHV-7 was the cause.���Patient 1 was a 6-year-old Japanese girl with encephalopathy who died one day after onset.���Patient 2 was a 4-year-old Japanese girl with encephalopathy whose absence of brainstem reflexes was confirmed and died 29 days after onset.���Patient 3 was a 22-month-old Japanese girl with myocarditis who managed with extracorporeal membrane oxygenation and survived but was left with severe neurological sequelae.���Because HHV-7 can cause serious outcomes in children, a virological search for HHV-7 in severe infections needs to be aggressive, and cases should be accumulated.
