OBJECTIVE To establish the value of repeat renal scans to assess the relative renal function after successful paediatric pyeloplasty. METHODS Renal scans were assessed from 138 patients after successful pyeloplasty; the relative renal function before and immediately after pyeloplasty were compared, as was split renal function at 3.5 and 5.5 years after surgery. RESULTS With a few exceptions the relative renal function before and after pyeloplasty was stable. Repeat renal scans 3.5 and 5.5 years after surgery also showed stable split renal function, even if the renal function was already diminished. CONCLUSIONS Repeat renal scans are not necessary after successful pyeloplasty in children, as most operated renal units showed stable renal function for 5-7 years. Further studies are needed to investigate whether renal function changes further after puberty.