We present a rare case of an unobstructed dilated renal pelvis in a newborn female. Prenatal imaging documented a large abdominal cyst in a stable fetus. Postnatal imaging confirmed persistence of this large cyst but with an unclear etiology. The child was taken to surgery by the pediatric surgeons with concern for a possible harmful nonurologic diagnosis. Intraoperative findings were that of a severely dilated renal pelvis; however, in the absence of an expected ureteropelvic junction obstruction. Reduction pyeloplasty without interference of the ureteropelvic junction proved successful.