A major complication of L-asparaginase used in the treatment of paediatric malignancies in children is pancreatitis (2%-16%). However, only seven paediatric cases of pancreatic pseudocyst caused by the utilization of the agent have been reported in literature. We present the case of a 5-year old girl who had abdominal pain and epigastric dullness after the third course of BMF-95 protocol with a diagnosis of ALL. A pancreatic pseudocyst of 10 x 10 cm size was found by abdominal tomography. The cyst was treated by percutaneous external drainage, total parenteral nutrition (TPN), administration of octreotide and antibiotherapy for one month. Percutaneous external drainage has proven to be an effective, noninvasive method in this special case with a systemic disorder and the high risk of mortality should a surgical intervention have been performed.