Endosalpingiosis refers to the presence of tubal epithelium outside the tube proper and is always an incidental finding. However, a few cases of tumor-like endosalpingiosis have recently been described (1,2). To our knowledge, only one case of tumor-like endosalpingiosis originating solely from the uterine serosa has been reported (2). Here, we describe one case of the two huge tumor-like masses of endosalpingiosis arising entirely from the uterine serosa, together with initial radiologic and clinical misinterpreted features. And the ultrastructural findings are reviewed. A 52-year-old woman, para 3-0-1-2, was presented with an accidentally detected pelvic mass from a periodic medical checkup. Transvaginal sonography (LOGIQ 500 Pro; GE, Wisconsin USA), Transducer [E721 wide band microconvex (4–9 MHz), Hardware: Motorola 68000 series] revealed multiseptated, complex cystic tumor adjacent to the uterus. Cystic and solid components are mixed, but cystic areas are mainly seen (Fig. 1). Malignant ovarian tumors could be considered as differential diagnoses. The computed tomography [SOMATOM sensation 16 (SIEMENS, New York, NY, USA)] showed two pelvic tumors with mixed cystic and solid areas adjacent to uterus. The tumors seem to be originated from both ovaries. The tumors are predominantly cystic and multiseptated. The uterus is deviated to left side by them (Fig. 2). Thus, serous or mucinous cystadenocarcinoma were suggested as differential diagnoses. Ovarian borderline malignant tumors also should be differentiated. In a laparatomy, two oval-to-round, reddish-colored, cystic and solid masses (13 × 12 × 11 cm and 9 × 7 × 7 cm, respectively) with short stalks were discovered in the right and left posterior fundal wall of the uterus. Also a 3 × 3 cm, whitish-pink mass was located in the anterior wall. Total abdominal hysterectomy with bilateral salpingoophorectomy was performed under the impression of uterine myomas with cystic degeneration. The uterus was pear shaped with three ovoid external protruding subserosal masses with narrow stalks. The larger two masses were located at the posterior side, measuring 13 cm and 8.5 cm in diameter, respectively. Both were thin-walled unilocular and multilocular cysts containing serous fluid. The smallest one was located on the anterior surface and appeared to be a subserosal myoma nodule. Microscopically, the larger two cysts were lined by an epithelium of tubal appearance. The epithelial lining was monolayer or multilayer with some foci of papillary infoldings. In some areas, the cells showed mild-to-moderate atypia such as an increased nuclear/cytoplasmic (N/C) ratio, hyperchromatic, and pleomorphic nuclei. No endosalpingiosis or endometriosis was present elsewhere. An ultrastructural examination showed a tube-like epithelium containing columnar, ciliated, and secretory cells. The ciliated cells showed numerous well-formed cilia and many glycogen granules. The smallest mass was subserosal leiomyoma. Transvaginal sonography showed multiseptated, complex cystic tumor adjacent to the uterus. Computed tomography showed bilateral cystic and solid tumor of the ovary. Endosalpingiosis was first described by Sampson (3) in his study of the stumps of 147 patients after tubal sterilization or previous salpingectomy. Endosalpingiosis most commonly involves the peritoneal surface of the uterus, fallopian tubes, ovaries, or cul-de-sac. Previously, a few cases of tumor-like endosalpingiosis arising in the uterine serosa have been reported. Clement and Young (1) reported four cases of endosalpingiosis manifested as masses that resembled neoplasm. Recently, Chang et al. (2) reported the first case of a multilocular cyst of endosalpingiosis originating solely from the uterine serosa. Our case is the second case of tumor-like cystic endosalpingiosis arising entirely from the uterine serosa. However, unlike the case of Chang et al., our case shows two huge uni-multilocular cystic masses of endosalpingiosis of the uterine serosa. And some papillary infoldings with the atypical mucosal changes of cyst are interesting features. Endosalpingiosis typically refers to the presence of histologically benign glands lined by a tubal-type epithelium involving the peritoneum and subperitoneal tissues. However, some cellular stratification, and varying degrees of cellular atypia rarely occur in endosalpingiosis, so-called ‘atypical endosalpingiosis’ (4,5), which can occur in cases of tumor-like cystic endosalpingiosis. In our case, some papillary infoldings and atypical mucosal changes were noted. But the atypism was mild and MIB1 staining showed a proliferation index less than 5%. An ultrastructural examination revealed cellnumerous cilia, glycogen granules, smooth endoplasmic reticulum (SER), and secretory granules, which are evidences of Mullerian differentiation. The interesting point in our case is that it shows radiologically the resemblance of ovarian malignant neoplasm and was misinterpreted as uterine myoma during the operation.