Meigs syndrome is defined by the presence of a benign ovarian tumor, ascites, and pleural effusion (predominantly on the right side). A characteristic sign of Meigs syndrome is the complete disappearance of exudate after surgical resection of the ovarian tumor.We present a case report of a 58-year-old patient admitted for an advanced ovarian tumor with pleural effusion, ascites, and tumor marker elevation typical for ovarian cancer. Cytological examination of ascites and pleural effusion was repeatedly negative for malignancy. Histopathological examination of the bio-psied tissue was concluded as low-grade mesenchymal neoplasia. The second opinion of histopathological examination was concluded as low grade fibroblastic pelvic tumor without the possibility of exact specification. Dia-gnoses of desmoid fibromatosis and low-grade fibromyxiod sarcoma (less likely) were considered. Surgical resection was indicated, and a large tumor with numerous adhesions to the uterus, bladder, and thin loops with a noticeably thickened peritoneum were perioperatively described. Histologically, left ovarian fibroma with productive peritonitis and sanguine-induced ascites was dia-gnosed. Due to the clinical findings and the result of the histopathological examination, the case was classified as Meigs syndrome. Two months after the surgery, the ascites and pleural effusion disappeared, and the tumor marker levels normalized.The present case report documents that it is always necessary to consider diseases other than those most likely at the outset, as the treatment algorithm and prognosis of these rare diseases may differ significantly.