Background: 18F-fluorodeoxyglucose-positron emission tomography (FDG-PET) adds to conventional imaging in the detection and staging of peritoneal carcinomatosis. Case report: Herein we report a 27-year-old woman with multiple intraperitoneal masses detected by 18F-FDG-PET, suggesting peritoneal carcinomatosis. She had undergone laparoscopic unilateral oophorectomy for a left ovarian mucinous borderline tumor approximately five years before. Based on imaging and intraoperative findings, multiple intraabdominal masses strongly suggested peritoneal recurrence from a previous ovarian borderline tumor, but it finally proved to be inflammation and fibrosis on histopathologic examination. Conclusion: Although 18F-FDG-PET is well known to be a highly sensitive imaging tool for identification of peritoneal carcinomatosis, FDG uptake is not tumor-specific. Therefore, the possibility of a falsepositive diagnosis due to benign conditions, such as inflammation, should always be taken into consideration.