Posterior urethral valves are the most common urethral obstructive disease in infants and neonates. The flap is usually located distal to the prostatic urethra and is formed by a mucosal fold that resembles a very thin membrane. The flap can cause varying degrees of obstruction during urination. What are the causes of urethral valves? The etiology of posterior urethral valve disease is unclear, as there is an occasional family history, and some believe it is the result of abnormal development of the mesonephric duct, or it may be the result of multiple factors, while others believe it is the result of abnormal development of the urogenital sinus. There are four theories for the formation of posterior urethral valves: 1, the distal and proximal ends of the normal seminal frenulum have several mucosal folds, if these mucosal folds are hypertrophic and protrude into the urethra, that is, the formation of type I or type II posterior urethral valves. 2, the urogenital membrane in the embryonic period did not completely recede, and the remnants of the urogenital membrane, that is, the formation of type III posterior urethral valves. 3, Congenital malformation of the mesonephric duct or Mullerian duct. 4, The mucosa of the seminiferous tubercle is fused with the urethral mucosa adhesions. It has been reported that all identical twin brothers have posterior urethral valves, and it is difficult to determine how this is related to heredity.