A family with 4 of 6 siblings manifesting vesicoureteric reflux is presented. Reflux could not be demonstrated in preceding and succeeding generations in this family. Genetic analysis suggests that most instances of familial vesicoureteric reflux arise secondary to expression of autosomal dominant single genes with incomplete penetrance. Screening of sibships for reflux might be most appropriately carried out by urine analysis, culture and ultrasound imaging.