The clinical findings and renal histopathology have been reviewed in children with gross primary vesicoureteric reflux (VUR) submitted to unilateral nephrectomy. Of the 42 children reviewed, sections of the nephrectomy specimens were available in 36. In this series, 34 patients were male and eight were female. The boys included seven in which hydronephrosis was identified by fetal ultrasound. The male patients tended to present earlier and had nephrectomies younger than the females. Segmental scarring was frequent in both males and females, but evidence of dysplastic renal development was confined to the male patients and occurred in the majority (63%). Acquired mechanisms for the induction of segmental renal scarring, involving VUR, intrarenal reflux (IRR) and urinary infection, shown to be important in older children, clearly operate in infancy. However, this study emphasizes that congenital malformation of the kidney is a crucial factor in the development of reflux nephropathy (RN) in this younger age group, particularly in males. Speculation on the significance of the association between renal dysplasia and RN is discussed in relation to observations on the embryological development of the male lower urinary tract.