['We determined whether the histology of upper pole nephrectomy specimens vary with prenatal detection or ureterocele position.', 'Between 1992 and 2000, 95 patients with ureteroceles associated with a duplex system underwent surgical interventions, including upper pole nephrectomy in 60. A total of 55 specimens, of which 25 and 30 involved a prenatal and postnatal diagnosis, and 18 and 37 involved an intravesical and extravesical location, respectively, were available for independent review by a single pathologist. Histological lesions were classified into the 5 categories of chronic interstitial inflammation, fibrosis, tubular atrophy, glomerulosclerosis and dysplasia. Each category was divided into moderate/severe histological lesions (greater than 25% involvement) and minimal/mild lesions (25% or less involvement).', 'A moderate/severe histological lesion was identified in 38 patients (69%) and a minimal/mild lesion was detected in 17 (31%), while dysplasia was present in 35 (64%). There was no significant difference in histological lesions and mode of presentation. In contrast to intravesical ureteroceles, extravesical ureteroceles were associated with severe fibrosis and tubular atrophy (p <0.05). Chronic interstitial inflammation, fibrosis, tubular atrophy and glomerulosclerosis in each specimen were graded moderate/severe (greater than 25% involved) in 55%, 67%, 66% and 53%, respectively.'] Is histology of upper pole unaffected by prenatal diagnosis in duplex system ureteroceles?