Background: Dandy-Walker malformation (DWM) is a rare congenital anomaly of the posterior fossa characterized by hypoplasia or agenesis of the cerebellar vermis, cystic dilatation of the fourth ventricle, and enlargement of the posterior fossa. It is frequently associated with hydrocephalus and various neurological deficits. Early diagnosis and appropriate intervention are essential for optimizing outcomes. Case Presentation: We present the case of a 1 year old female child who presented with progressive macrocephaly, irritability, vomiting, and delayed developmental milestones. Neuroimaging revealed classical features of DandyWalker malformation, including partial agenesis of the cerebellar vermis, a large retrocerebellar cyst communicating with the fourth ventricle, and dilated lateral and third ventricles indicative of associated hydrocephalus. Management and Outcome: The patient underwent successful cystoperitoneal (CP) shunt placement to divert cerebrospinal fluid from the posterior fossa cyst to the peritoneal cavity. Postoperative recovery was uneventful, with gradual reduction in head circumference and improvement in feeding and irritability. Followup imaging demonstrated decompression of the cyst and reduced ventricular size. The patient continues to receive multidisciplinary follow-up, including neurodevelopmental monitoring and rehabilitation. Conclusion: This case underscores the importance of timely neuroimaging in infants with progressive macrocephaly and developmental delay. Cystoperitoneal shunting remains an effective surgical option in managing hydrocephalus associated with Dandy-Walker malformation. Early intervention may contribute to favorable developmental outcomes, although long-term prognosis largely depends on the extent of associated anomalies and overall cerebral development