BACKGROUND Meigs' syndrome consists of a benign ovarian tumor accompanied by ascites and hydrothorax. Elevated serum CA 125 levels in postmenopausal women with solid adnexal masses, ascites and pleural effusion are highly suggestive for malignant ovarian tumor. However, patients with Meigs' syndrome can also have elevated serum CA 125 levels. The authors report a case of Meigs' syndrome with elevated CA 125 level. OBJECTIVE This is a case report of Meigs' syndrome with elevated CA 125 level. METHODS A 65-year-old Brazilian woman had presented progressive dyspnea, weight loss and decline in general condition over the 7 months preceding admission to our service. In another hospital, the patient had been submitted to thoracic drainage due to pleural effusion. With recurrence of the pleural effusion and increase in abdominal volume due to ascites and a pelvic mass, the patient sought our service. Transvaginal ultrasound showed an extensive adnexal solid mass of 16.4 x 10.8 cm located in the pelvis without exact limits, and the serum CA 125 level was elevated. With a preoperative diagnosis of ovarian carcinoma, the patient was submitted to exploratory laparotomy, which revealed a left ovarian tumor. The frozen section diagnosis was thecoma. Total abdominal hysterectomy with bilateral salpingo-oophorectomy was performed. The histology of the specimen confirmed the diagnosis of thecoma. The patient was asymptomatic with a normal serum CA 125 level 20 months after the operation.