Cystadenomas and cystadenocarcinomas are rare but not exceptional tumours of the pancreas. In this report six cases are added to the more than 300 cystadenomas and over 100 cystadenocarcinomas reported in the literature. We present here the case histories of four cystadenomas and two cystadenocarcinomas with complete follow-up. There is no evidence of recurrence after a maximum of 22 years in cystadenoma and 4 years in cystadenocarcinoma following resection. We have the impression that cystic lesions of the pancreas are nowadays more often detected than in former years. This might be due to abdominal investigation by computerized tomography and ultrasound on a large scale. Pathological features of proliferative cystic lesions of the pancreas permit distinction of three different tumours: serous cystadenoma, mucinous cystadenoma and cystadenocarcinoma. The serous cystadenoma is benign. The mucinous cystadenoma has to be considered as potentially malignant. The cystadenocarcinoma is malignant by definition. As benign and malignant elements can be found in the same cyst biopsy cannot exclude cystadenocarcinoma. Therefore all cystadenomas and cystadenocarcinomas should be totally excised, especially as prognosis after resection of cystadenocarcinoma is much better than after resection of adenocarcinoma of the pancreas.