A 10-year-old boy was admitted with blunt abdominal trauma by bike handle injury. The patient was operated upon for a generalized peritonitis due to pancreaticoduodenal injury. On opening the peritoneal cavity, complete transection of distal end of common bile duct and, partial separation between pancreas head and second portion of duodenum were found. Ligation of the transected end of the common bile duct, T-tube choledochostomy, and external drainage were performed. A pseudocyst was found around the head portion of the pancreas on the 7th postoperative day with CT. An internal fistula had developed between the pseudocyst and ligated common bile duct. The pseudocyst was subsided after percutaneous drainage. In the case of the undetermined pancreatic injury, percutaneous external drainage can be effective in treating the traumatic pancreatic pseudocyst in a pediatric patient.