Pancreatic pseudocysts are a complication of both acute and chronic pancreatitis that usually develop four to six weeks from the onset of pancreatitis. Alcoholic pancreatitis is the most important risk factor for developing such cysts, although non-alcoholic cases do also occur. This is the case of a 58-year-old male patient who presented to our emergency department with a two-day history of abdominal pain, nausea, vomiting, and inability to tolerate oral food and liquids. His initial labs showed significantly elevated lipase and triglycerides. A computed tomography (CT) scan showed extensive, ill-defined pancreatic enlargement with inflammatory changes consistent with severe acute pancreatitis. Following his hospital course, on day 15, a CT abdomen/pelvis with contrast showed a new, huge pseudocyst anteriorly from the pancreas measuring 9.5 × 18 × 15 cm that rapidly progressed to 25.5 × 17.7 × 22 cm in a week with a significant mass effect. No previous sign of pseudocyst existed before this time, indicating rapid progression. Drainage and subsequent necrosectomy with stent placement were subsequently performed. To the best of our knowledge, this is the first instance of such a rapid progression of pancreatitis to large pseudocyst formation.