Leiomyomatosis peritonealis disseminata (LPD) is an uncommon condition characterized by multiple nodules of smooth muscle within the peritoneal cavity. It usually occurs during reproductive age, and is especially associated to exogenous and endogenous exposure to female gonadal steroids. A limited number of cases of malignant transformation have been reported in the literature. We report a case of leiomyomatosis peritoneais disseminata with sarcomatous degeneration in a 37-year-old nulligravid patient with no exposure to exogenous estrogen or progesterone, revealed by increased abdominal perimeter. The imaging techniques showed occupation of the entire peritoneal cavity by bulky solid masses. The patient underwent a total hysterectomy with bilateral salpingo-oophorectomy and tumoral mass resection. The histopathologic diagnosis was leiomiomatosis peritonealis disseminata with leiomyosarcomatous degeneration. The patient was given systemic chemotherapy with tumoral progression, and died 24 months after the initial diagnosis.