Congenital abnormalities of the kidney and urinary tract (CAKUT) account for more than half of all renal failure in children. For young adults with CAKUT two questions are paramount: what is the prognosis and what is the best management to improve outcome? The paediatric literature shows that prognostic factors are glomerular filtration rate (GFR) and the presence of proteinuria. We reviewed data from 101 young adult patients with either primary vesico-ureteric reflux and renal dysplasia or obstructive uropathy. Patients had an estimated GFR (eGFR) of <or=60 ml/min per 1.73 m(2) body surface area and had had at least 5 years of follow up (median 162 months). There was a strong correlation between the amount of proteinuria at the start and overall rate of decline. Angiotensin-converting enzyme inhibitors (ACEIs) slowed declining renal function at all levels of function, but this only had a significant effect on renal outcome when eGFR was >35 ml/min. The ACEI benefit increased with time. Rate of decline was slower than reported for other diseases and was only -2.4 ml/min per year for those reaching the start of dialysis. Outcome is predictable by the level of residual renal function (GFR). Nevertheless, function remains stable while proteinuria is minimal. Short-term studies overestimate rates of deterioration.