A 32-year-old woman, gravida 4, para 2, was diagnosed with a benign right ovarian mucinous cystadenoma. It was diagnosed in the tenth week of pregnancy, measured 47 x 69 mm, and reached 190 x 152 mm at 23 weeks of gestation. Laparotomy was performed and the ovarian cystic mass was removed in the second trimester. The patient had postoperative tocolytic therapy and progesterone medication. She is at the 35th gestation week and no other antenatal complication has been reported. A case of giant mucinous cystadenoma is presented with clinical follow-up details.