At 24 weeks of gestation, a fetus was suspected of having a huge intraabdominal cyst by fetal ultrasound. Multicystic dysplastic kidney (MCDK) was the most probable diagnosis; however, because a solid area was visualized in the large cystic lesion, a neoplasm of the kidney could not be ruled out. A 3529-g boy was born at 35 weeks of gestation by cesarean delivery. Eight days after birth, the tumor was resected. Histopathologic examination confirmed MCDK. The cause of MCDK in this patient was assumed to be ureteral obstruction in early fetal life. These findings suggested that the affected kidney had experienced mesenchyme-to-epithelium transition followed by interaction between the metanephric blastema and ureteral bud.