The variable effect of posterior urethral valves as illustrated in identical twins.

To our knowledge, we report the second instance of posterior urethral valves in identical twin boys. Initial symptoms, age at presentation and radiographic findings were different in each boy, and reflect the varying nature of this congenital anomaly. Although the brothers are identical twins from the same environment with identical Rh and ABO blood groupings and identical HLA haplotypes, developmental differences have been marked.