Adenosquamous carcinoma of the pancreas is a rare form of pancreatic cancer. Its biological behavior and clinical features are known to be similar to the much more common ductal adenocarcinoma or to pure squamous cell carcinoma, another rare form of pancreatic malignancy. However, the unusual manifestations of cancer, including cystic degeneration and extravasation of contrast to the mass, have also been reported. A 64-year-old man was admitted complaining of abdominal pain. An abdomial CT scan demonstrated an ovoid and cyst-like lesion in the pancreatic head and endoscopic retrograde balloon pancreatography showed segmental narrowing of the main pancreatic duct associated with extravasation of contrast into the cyst-like lesion. Under the impression of pancreatic pseudocyst with chronic pancreatitis, medical therapy including pancreatic stent insertion was given to the patient for four weeks. Finally, a laparotomy was performed due to persistent abdominal pain and a poorly demarcated mass with cystic cavity was resected. Histologic findings were consistent with adenosquamous carcinoma of the pancreas. The unusual features of this rare malignancy which led us to an errorneous initial diagnosis were emphasized. (Korean J Gasitrointest Endosc 18: 129-133, 1997)