We report a 7-year-old Taiwanese girl with acute pancreatitis (AP) complicated with pseudocyst (PC). The girl was found to have a PC by ultrasonograpgy (USG) and magnetic resonance imaging 14 days after the onset of AP. The girl was discharged 21 days after management with an asymptomatic PC. The diagnostic criteria of AP included abdominal pain, serum amylase or lipase level, and imaging findings. Transabdominal USG after appropriate preparation with adequate fasting, intake of some liquids during the scanning, and right decubitus position enhance the demonstration of pancreas and peripancreatic structures. PC could be seen in up to 38% of pediatric AP patients. It can form within 2 weeks after the onset of symptoms, although most are late complications. Pancreatic PCs have to be differentiated from other intra-abdominal cysts on USG according to their image character and anatomic location. A well-prepared USG examination in combination with liquid intake and right decubitus position is of value in the diagnosis and follow-up of PC.Abbreviations: ANC, acute necrotic collection; AP, acute pancreatitis; APFC, acute peripancreatic fluid collection; CECT, contrast-enhanced computed tomography; CRP, C-reactive protein; CT, computed tomography; MRI, magnetic resonance imaging; PAP, pediatric acute pancreatitis; PC, pseudocyst; USG, ultrasonography.