Ovarian thecoma, which belongs to the group of sex-cord stromal tumors, is a relatively rare neoplasm. In this report we present a pregnant woman with a solid ovarian mass diagnosed during pregnancy and operated on at the 19th gestational week. At surgical exploration, torsion of the ovarian tumor was observed together with ascites and unilateral salpingo-oophorectomy was performed. Pathological examination revealed a luteinized thecoma. After the surgery, the pregnancy continued uneventfully until term.