BACKGROUND The aims of this report were to describe a case of ovarian adenosquamous carcinoma and to systematically review the pertinent literature. METHODS We describe a case in which a 57-year-old woman had stage IC ovarian cancer histologically diagnosed as adenosquamous carcinoma. We also systematically reviewed the literature using the PubMed database. CASE PRESENTATION Preoperative computed tomography and magnetic resonance imaging showed a tumor measuring 14 cm in diameter and containing solid areas. Tumor marker levels were as follows: CA125, 42.6 U/mL; CA 19-9, 134.1 U/mL; CEA, 0.9 ng/mL; and SCC, 1.6 ng/mL. The patient underwent multiple surgeries including total abdominal hysterectomy, bilateral salpingo-oophorectomy, pelvic lymph node dissection, para-aortic lymph node biopsy, and total omentectomy. Based on the cytological features of the ascitic fluid, the tumor was diagnosed as a squamous cell carcinoma. Histological examination of an excised specimen showed the transition of an endometrioid adenocarcinoma to a squamous cell carcinoma. There was no evidence of any teratomas or endometriosis-related features. We considered the tumor to be an adenosquamous carcinoma, with the squamous cell carcinoma component arising from the endometrioid adenocarcinoma component. After surgery, the patient underwent 6 cycles of paclitaxel and carboplatin chemotherapy. There has been no recurrence to date, 66 months after the initial treatment. RESULTS Histologically, the 8 adenosquamous carcinomas reported in the literature either arose from the mature cystic teratoma (4 cases) or endometriosis (3 cases) or were pure adenosquamous carcinomas (1 case). Our literature search uncovered no cases of ovarian adenosquamous carcinomas originating from endometrioid adenocarcinomas. CONCLUSIONS This is the first reported case of an adenosquamous carcinoma arising from an endometrioid adenocarcinoma. Because such tumors are rare, their standard management is unclear.