Seborrheic inclusion cyst is an unusual variant of epidermal cyst characterized by parietal histology similar to seborrheic keratosis. Cysts with such changes have been called "seborrheic keratosis-like changes in epidermal cyst" or "epidermoid cyst with seborrheic verruca-like cyst wall" or simply "seborrheic cyst". To date, this lesion has been described exclusively in cutaneous sites. We describe the first case of an extracutaneous seborrheic inclusion cyst arising from round ligament. A 30-year-old female was referred to our institution for abdominal pain. Ultrasonography showed a hypoechoic heterogeneous, round mass adjacent to the lower extremity of the left ovary, measuring 4.5 cm in maximum diameter. Contrast-enhanced computed tomography of the pelvis in the venous phase showed a round (4.5 cm in diameter) cystic lesion with inhomogeneous fluid content in the side of the left large ligament and anterior to the homolateral adnexa. Laparoscopic resection of the mass was performed. Intraoperatively, an extraperitoneal glistening pelvic mass was discovered: the lesion was attached to the intrapelvic 1/3 middle portion of the left round ligament. Macroscopically, the mass measured 6 cm x 6 cm x 3.5 cm and exhibited a smooth and glistening external surface. On cut sections, the mass was an unilocular cyst filled with soft, yellow, amorphous material. Histologically, the cystic wall was lined by a stratified squamous epithelium with a granular cell layer. The cavity contained keratin-like material. The cystic wall showed numerous areas with close-set basaloid cells and pseudohorn cysts. The latter aspect consisted of cystic invaginations of the epithelium filled with surface keratin, which in a given microscopic section may be cut in cross-section, thereby appeared as "cysts" within the involved epithelium. Parietal rupture was present, accompanied by granulomatous inflammation. There were no postoperative complications, and the patient was discharged 3 days after the procedure. The present case is unique in that it is the first reported case of an extracutaneous seborrheic inclusion cyst arising from a very unusual site, namely the round ligament. The site of origin of the lesion and its cystic nature were established by computed tomography findings. Conservative treatment with enbloc resection was possible. Histological examination confirmed computed tomography findings. The present report described a lesion typically found in dermatopathology practice, but which had arisen in an extracutaneous site.