A 26-yr-old woman (Para: 0-0-0-0) was referred to the breast clinic for the management of bilateral breast enlargement that she experienced at 29 weeks of gestation. The progressive enlargement of both breasts started at 6 weeks of gestation. She also had pain on both her breasts, her shoulders and her back and accompanying skin lesions. On physical examination, the skin over the breasts was red and edematous, with overlying dilated veins. Also on the left side, a patch of desquamation and ulcerative lesion was noticed. Ultrasonography of the breasts showed bilateral parenchymal enlargement with vessel engorgement and ductal dilatation. A 4.2 cm sized well-circumscribed probably benign oval hypoechoic nodule (BI-RADS Category 3) was identified at the upper inner quadrant of the left breast. The patient was conservatively managed until the end of her pregnancy. She delivered a normal full-term baby at 39 weeks of gestation. She did not breast-feed the baby due to severe pain and she revisited the breast clinic at 4 months after the delivery. The size of both breasts was markedly decreased compared to that at the initial visit and the skin lesions on her left breast were completely healed. We report here on the first case of gestational gigantomastia that was treated with conservative care in Korea.