Arachnoid cysts are benign developmental anomalies that occur in the cerebrospinal axis in relation to the arachnoid membrane. An antenatal ultrasound scan first raises the suspicion of arachnoid cysts, but misdiagnoses have been reported. Confirmatory antenatal magnetic resonance imaging (MRI) is very useful to delineate anatomical detail and help in correct diagnosis. This helps proper counselling and treatment planning. Controversy also surrounds the surgical management, in terms of both the indications and the procedures employed. We report the successful endoscopic treatment, in a neonate, of an arachnoid cyst diagnosed by antenatal ultrasound and MRI. In this case accurate diagnosis and detailed assessment led to objective counselling and helped to optimise neonatal management.