Following the diagnosis of primary vesicoureteric reflux, identified as part of the investigation of urinary tract infection, 299 refluxing kidneys in 202 children (aged 0-14 years) were prospectively evaluated using intravenous urography (IVU) and the DMSA renal scan at least 4 weeks after urine infection. There was 88% concordance between IVU and the DMSA scan, but in 12% there were discrepancies manifested in 37 kidneys from 31 children. Thirty-four kidneys were normal on IVU but showed scars of reflux nephropathy (RN) on the technetium 99m--dimercaptosuccinic acid (DMSA) renal scan; 4 of these (2 infants and 2 pre-school children) had severe generalized changes on scanning. Three kidneys were normal of DMSA scan and, although abnormal on initial IVU, were considered to be normal when this was repeated. During a follow-up period of 5 years an annual DMSA was undertaken in 194 patients and the renal scars remained unchanged in all except 1 child. The IVU was repeated 1-3 years after the initial study in 31 children in which the results of the first imaging did not agree. In 28 patients (34 kidneys) in which the initial IVU was normal but the DMSA abnormal, IVU evidence of scarring emerged in 30 of 34 kidneys, including the 4 patients with severe generalized damage on the DMSA. We conclude that abnormalities detected by the DMSA scan may precede the radiological findings, especially in young children. Even severe RN can be established in kidneys that appear normal on the IVU.