Introduction and importanceMullerian adenosarcoma is a rare malignancy that generally occurs in the uterine corpus but uncommonly, it may be found extrauterine. Ovarian adenosarcoma is extremely rare and often is presented in reproductive age women. Most of them are low grade and have à good prognosis except for adenosarcoma with sarcomatous overgrowth.Case presentationA 77-year-old menopausal woman presented with abdominal discomfort. She had severe ascites and elevated levels of CA-125, CA 19-9, and HE4 tumor markers. Adenosarcoma with sarcomatous overgrowth was diagnosed after the histopathological examination of the surgical biopsy.ConclusionThe possibility of endometriosis transformation to malignancy even in postmenopausal women may warrant continuous follow-up for early diagnosis of ovarian cancer, this potentially fatal disease. More studies are needed to find the best therapeutic approach to adenosarcoma with sarcomatous overgrowth.