To find out whether preoperative morphological investigations differentiated between serous cystadenoma, mucinous cystadenoma, and cystadenocarcinoma of the pancreas. Multicentre retrospective study of casenotes. 24 Adult gastroenterology units (1 private, 8 non-university teaching hospitals, and 15 university teaching hospitals) in France. 71 Patients with 74 tumours diagnosed between January 1978 and January 1988. Correlation between histological diagnosis and results of ultrasonography, computed tomography, angiography, and magnetic resonance imaging. 6 of 59 ultrasound scans (10%), 7 of 52 computed tomograms (13%), 0 of 18 angiograms, 1 of 12 pancreatograms (8%), and the single magnetic resonance scan correctly diagnosed the type of pancreatic tumour. Ultrasonography or computed tomography, or both, diagnosed cystadenoma (but not the type) in 26 cases (37%). "Pseudocyst" was diagnosed in 14 cases (20%). In contrast to other studies, our results indicate that preoperative morphological investigations are of limited value in diagnosing cystadenomas of the pancreas. In particular, their ability to differentiate between different types of cystadenoma is poor.