We report 3 cases of benign mucinous cystadenoma of the pancreas mimicking, both clinically and on imaging findings, locally advanced cystadenocarcinoma spreading to neighbouring organs (stomach, splenic and mesenteric vessels, and diaphragm). Surgical resection was performed in light of the suspicion of invasive carcinoma in all 3 cases. Histological examination of the resected specimens showed entirely benign mucinous cystadenomas associated with marked peri-tumoural inflammation that accounted for the pre-operative misdiagnoses. All 3 patients are alive 40, 47 and 54 months after surgery without evidence of tumour relapse. These cases indicate that surgery must be considered in patients with cystic tumour of the pancreas suggesting locally advanced cystadenocarcinoma, even when pre-operative imaging findings suggest tumour extension into neighbouring organs.