A case of double bilateral renal vessels in both twins of a MZ pair is reported for the first time. Even in non-twins, the anomalies reported so far involved the inferior polar arteries in agreement with the embryological development. The two male twins, examined at the age of 14 years, had simultaneously developed a marked hypertension at the age of 7 years. Zygosity was determined by blood group and HLA analysis and various clinical tests were carried out to diagnose the condition. It is suggested that the anomaly is the result of a genetically induced early block in embryonic development.