We present 3 cases in which a neonate had unilateral hydronephrosis associated with a ureter hypoplastic throughout its length. In all 3 infants the affected kidney failed to visualize on excretory urography and function of the kidney proved to be disappointing despite its relatively normal appearance on external examination. In each case significant renal dysplasia was present microscopically and ultimately the kidney had to be removed. A retrograde pyelogram should be considered whenever a hydronephrotic kidney in an infant fails to visualize, and if this shows a long hypoplastic ureter that cannot be bypassed easily associated renal dysplasia should be suspected and consideration given to nephrectomy rather than pyeloplasty as the primary treatment modality.