Primary vesicoureteric reflux (VUR) was detected by prenatal sonography in 34 infants (55 renal units); males accounted for 31 cases. Associated genitourinary anomalies were common, occurring in 29% of the patients. Some element of hydroureteronephrosis was noted at initial cystography in 89% of refluxing renal units, but the degree of renal abnormality at 99Tc DMSA renography was not predicted by the severity of VUR. Overall, 60% of refluxing renal units were renographically abnormal. Although a high rate of urinary infection was encountered during follow-up, most DMSA assessments were carried out prior to infection and hence likely reflect congenital rather than acquired abnormalities. It was concluded that renal impairment associated with high grade primary VUR is frequently present at birth and not secondary to subsequent infection.