Abstract Congenital giant megaureter presents as abdominal mass and impose diagnostic difficulties. It can be associated with other upper urinary tract anomalies. A female newborn with antenatal diagnosis of polycystic kidneys was admitted at birth due to lower abdominal mass. Ultrasound and CT scans diagnosed a multiloculated cystic lesion in the mid and lower abdomen along with right side multicystic kidney. At laparotomy, an extaperitoneal, lobulated cystic swelling was found due to rightside giant megaureter. Its lower end was of normal caliber and orthotopic. End cutaneous ureterostomy was done. Intravenous urogram and isotope renograms showed nonfunctioning right kidney. She also had grade II vesicoureteral reflux on left side. Child suffered urinary infection twice. At 9m age, right nephroureterectomy was done. Histopathologic examination was consistent with cystic renal dysplasia and dilated ureter. This is the first case report of giant megaureter associated with ipsilateral multicystic dysplastic kidney in newborn