Pancreatic cancer is sometimes called a "silent disease" because it often causes no symptoms in the early stage. The symptoms can be quite vague and various depending on the location of cancer in the pancreas. The anatomic site distribution is 78% in the head of the pancreas, 11% in the body, and 11% in the tail. Pancreatic cancer is rarely detected in the early stage, and it is very uncommon to diagnose pancreatic tail cancer during an emergency department visit. The manifestation of pancreatic tail cancer as left flank pain is very rare and has seldom been identified in the literature. We present a case of pancreatic tail cancer with the sole manifestation of dull left flank pain. Having negative findings on an ultrasound study initially, this female patient was misdiagnosed as having possible acute gastritis, urolithiasis or muscle strain after she received gastroendoscopy and colonofiberscopy. Her symptoms persisted for several months and she visited our emergency department due to an acute exacerbation of a persistent dull pain in the left flank area. Radiographic evaluation with computed tomography was performed, and pancreatic tail tumor with multiple metastases was found unexpectedly. We review the literature and discuss this rare presentation of pancreatic tail cancer.