Context Pancreatic acinar cystadenomas are rare cystic lesions that show acinar differentiation and follow a clinically benign course. Few previously reported acinar cystadenomas have demonstrated focal mucinous metaplasia. Although debatable, ACAs are considered to be neoplastic. Case report We present a case of a sixty-three-year-old man who underwent total pancreatectomy for a diffuse, multilocular acinar cystadenoma with multifocal branch-duct intraductal papillary mucinous neoplasm with moderate dysplasia. Histologically, the lesion was composed of variably sized cysts lined predominantly by cuboidal and focally flattened acinar cells with some cysts lined solely by mucinous epithelium. Overt evidence of acinar differentiation adjacent to the cysts was identified and composed of dilated and interconnected acini communicating with the cysts. Scattered mural nodules composed of acinar cells were present throughout the pancreas. There was no significant nuclear atypia or mitotic activity seen in the acinar component. Eosinophilic lamellated concretions, club-like pseudopapillae, and focal squamous metaplasia were noted in some cysts. In addition, focal metaplastic ossification and patchy minute foci of calcifications were present within the acinar cystadenoma. About 30% of the lesion showed areas of branch-duct intraductal papillary mucinous neoplasm with focal areas of moderate dysplasia. The residual pancreas contained multifocal areas of pancreatic intraepithelial neoplasia 1. Conclusion This finding supports the classification of multilocular acinar cystadenoma as a neoplastic lesion predisposing to both intraductal papillary mucinous neoplasm and pancreatic intraepithelial neoplasia. Although benign, complete resection may be needed for diffuse, multilocular lesions given the potential presence of dysplasia.