INTRODUCTION: Abdominal pseudocysts comprising cerebrospinal fluid are an uncommon but significant complication in patients with ventriculoperitoneal shunt. We present a successfully treated 12-year-old boy with a history of ventriculoperitoneal shunting and a huge abdominal cerebrospinal fluid pseudocyst. CASE PRESENTATION: A12-year-old Japanese boy presented with a deteriorated consciousness and a palpable and elastic large lower abdominal mass. Computed tomography of his abdomen demonstrated a collection of homogenous low-density fluid near the catheter tip of the ventriculoperitoneal shunt. Cerebral computed tomography revealed an increased ventricular size. Based on the clinical diagnosis of abdominal pseudocyst, the peritoneal shunt catheter was secured and divided into two parts by cutting it on the chest; then, the proximal side of the peritoneal shunt catheter was externalized for extraventricular drainage. The cyst was percutaneously aspirated with ultrasound guidance, and the distal side of the peritoneal shunt catheter was removed. The distal side of the peritoneal shunt catheter was reinserted in another position into his abdomen after 3-week extraventricular drainage management. CONCLUSION: Emergency physicians should know about this potential complication as an important differential diagnosis resulting from acute abdominal complaints in patients with ventriculoperitoneal shunts.