The diagnosis of intraductal papillary mucinous neoplasms (IPMNs) of the pancreas includes radiographic (CT, MRI) and endoscopic evaluation (ERCP, EUS). The treatment strategy is outlined in the 2012 International Consensus Guidelines (ICG). Herein, we report a case initially not indicated for surgery. Four months after the initial diagnosis, the cystic lesion transformed into a solid mass-like lesion visible on CT. FDG-PET showed abnormal FDG uptake at the same location. Surgical resection was performed immediately, and the tumor was diagnosed as IPMN with inflammation. FDG-PET showed a false-positive diagnosis for the malignancy in this case of IPMN.