Acute pancreatitis is only rarely the first presentation of a cystic neoplasm of the pancreas. Mucinous cystadenomas have not been reported to be a cause of acute pancreatitis; however, we present two cases of mucinous cystadenoma of the pancreas which have caused acute pancreatitis. Both patients (female) presented acute abdominal pain, with serum amylase elevation and ultrasound scan (US) and computed tomography (CT) evidence of moderate pancreatitis, which resolved with medical treatment; fluid collection in the distal pancreas had been misinterpreted as a pseudocyst. There was no history of alcohol abuse or gallstone disease. After distal pancreatectomy the diagnosis of mucinous cystadenoma was confirmed; in one case a large pseudocyst was associated with this diagnosis. Pre-operative differential diagnosis between inflammatory and neoplastic cysts is difficult, especially when the patient's first presentation is due to an episode of acute pancreatitis. A neoplastic cyst should be considered when acute pancreatitis attacks occur in non-alcoholic women, who do not have gallstone disease.