Childhood intracranial aneurysms are exceedingly uncommon. Diagnosis of intracranial aneurysms in infancy may be difficult because of their infrequency and confusing clinical presentation. Findings with routine radiographic methods may be misleading and difficult to interpret. We present a case of the rupture of an anterior communicating artery aneurysm in a 7-month-old child. The rupture had eluded diagnosis until contrast-enhanced MR imaging was performed.