Encephalitis is the inflammation of the brain parenchyma accompanied by mental or behavioral neurological dysfunction, sensory or motor deficits, speech or movement disorders, and seizure. Encephalitis is an acute, life-threatening emergency that requires prompt recognition and a systematic approach for appropriate management. Human herpes virus (HHV-7) is one of the causative agents of encephalitis. In this report, a three years and six months old girl admitted to the hospital with the complaints of fever, cough, gushing vomiting, and altered consciousness, with fever, neck stiffness and blurred consciousness in her physical examination, and positive HHV-7 DNA polymerase chain reaction (PCR) in the cerebrospinal fluid (CSF) was presented. The CSF biochemistry of the patient was normal, and lymphocytic pleocytosis was detected in the CSF. Electroencephalography of the case revealed a cerebral dysfunction and hyperexcitability due to background activity abnormalities, and a cytotoxic transient lesion of the splenium in cranial magnetic resonance imaging. A 14-day foscarnet treatment was given to the patient after she progressed under empirical acyclovir treatment and HHV-7 was found to be the causative agent in the CSF. The patient was cured with the treatment and was followed up on an outpatient basis without any sequelae. In general, HHV-7 is estimated to be a common cause of pediatric acute encephalitis cases. It has been observed in the literature that almost all of the HHV-7-associated encephalitis cases occur after the age of six years, suggesting that HHV-7 causes neurological disease in children as a late infection. This case was three years and six months old and it was thought that she had encephalitis during primary infection. With this case report, we contributed to the literature by presenting a case of encephalitis in an immunocompetent pediatric patient with a transient splenial lesion associated with HHV-7, which progressed with empirical acyclovir treatment and responded to foscarnet treatment.