Arachnoid cysts are relatively common and benign intraarachnoid membrane outpouchings containing CSF-like fluid. The majority of arachnoid cysts remain stable and asymptomatic and do not require intervention in the pediatric population. Here, the authors present the first reported case of an infected arachnoid cyst in a pediatric patient resulting in severe vasospasm of the left terminal internal carotid artery, left A₁ segment, and left M₁ branches with a left middle cerebral artery infarct. Their experience suggests that close monitoring is warranted for this condition and that the pediatric population may be at higher risk for vasospasm.