A previously healthy 7-month-old male presented to the emergency department with fever and a bulging anterior fontanelle. A computed tomographic scan of the head suggested mild communicating hydrocephalus. Lumbar puncture was performed, which revealed a normal cerebrospinal fluid (CSF) cell count and glucose concentration, but a markedly elevated opening pressure. DNA polymerase chain reaction for herpes simplex virus performed on CSF was negative; CSF bacterial cultures were without growth. DNA polymerase chain reaction for human herpes virus 6 was strongly positive in serum. Fever and bulging fontanelle resolved within 24 hours. A presumptive diagnosis of transient intracranial hypertension of infancy was made, a form of benign idiopathic intracranial hypertension that mimics the presentation of serious intracranial pathology.