ABSTRACT Introduction: Due to the destructive nature of pancreatic enzymes, a pseudocyst can extend into abdomen, mediastinum more commonly and intrahepatic parts, intercostal space, lumbar region rarely. In literature, only 5-6 case reports of this rare presentation, Pancreatic psudocysts presenting as lumbar mass have been reported. Case: A forty-five years old gentleman, known chronic alcoholic, presented with a painful swelling over left flank region for 8 days. On examination, A cystic swelling of approximately size 10x8 cm was present over left lumbar region, having no local rise of temperature, cystic in consistency, fluctuant and non-tender. USG (A+P) was suggestive of cystic swelling with purulent collection differential diagnosis being? Infected pancreatic pseudocyst or? infected urinoma. CECT A +P was s/o subacute focal pancreatitis involving tail region with infected multiloculated pseudocyst involving left anterior pararenal, posterior pararenal, perinephric spaces, posterior paraspinal muscles and left kidney. This case was managed by external drainage using USG guided percutaneous Pigtail catheter insertion Discussion: Pancreatic pseudocyst must be differentiated from other cystic retroperitoneal swellings. Ultrasound (USG) is initial diagnostic tool with sensitivity rates for USG in the detection of pancreatic pseudocysts are from 75% to 90%. But, Computerized tomography (CT) is often the imaging method of choice, with 82% to 100% sensitivity and 98% specificity. Conclusion: A differential diagnosis of pancreatic pseudocyst should be considered especially in known chronic alcoholic patients and known patients with previous history of pancreatitis. Percutaneous drainage procedures with pigtail catheter insertion, less invasive than internal drainage with laparotomy or other interventional procedures, hence reduces morbidity due to easy accessibility.