Pancreatic pseudocyst develops as a complication of both acute and chronic pancreatitis. Although the common location of pseudocyst is lesser sac, extension of pseudocyst can occur into mesentery, retroperitoneum, inguinal region, scrotum, liver, spleen, mediastinum, pleura, and lung. Extension of pseudocyst into psoas muscle and lumbar triangle is extremely rare. The development of pseudocyst in lumbar triangle is radiologically equivalent and further extension of Grey Turner's sign seen clinically in acute pancreatitis. This extension occurs due to the destructive nature of pancreatic enzymes. The lumbar triangle is the site of anatomic weakness in the lateral abdominal wall in the lumbar region. We report the case of a 35-year-old alcoholic male patient who presented with abdominal pain followed by distension and swelling in the right lumbar region for 1 week. On computed tomography scan of the abdomen, acute-on-chronic pancreatitis with multiple pseudocysts in the right posterior pararenal space, extending through the right lumbar triangle in the right lateral abdominal wall, right posterior paraspinal muscles, right iliopsoas, right obturator externus, and medial aspect of the right upper thigh, beneath anterior abdominal wall in the upper abdomen and in the right lateral thoracic wall through the right 11th intercostal space, was detected.