We report a case of fallopian tube and peritoneal lesions resected from a 10-year-old girl with Proteus syndrome. The papillary fallopian tube tumor expressed CA-125 and demonstrated negative staining for CEA, CD15, calretinin, and CK 5/6. Nondilated portions of fallopian tube exhibited evidence of an in situ component. This patient was also found to have peritoneal mesothelial hyperplasia as well as cystic peritoneal lesions of mesothelial origin, with positive calretinin staining. This case provides direct evidence of both Müllerian and mesothelial lesions arising concurrently in a patient with Proteus syndrome and represents the 1st documented fallopian tube neoplasm. Previously reported lesions involving the female and male genital tracts in patients with Proteus syndrome are reviewed.