Most common cause of urinary obstruction in a male infant is:

Posterior urethral valve is the most common cause of urinary obstruction in a male infant. Urethral valves are mostly posteriorly located, anterior urethral valve are usually associated with congenital urethral diveiculum. Renal calculi and stricture are uncommon in children. Ref: Kliegman, Behrman, Jenson, Stanton (2008), Chapter 540, "Obstruction of urinary tract", In the book, "NELSON TEXTBOOK OF PEDIATRICS", Volume 2, 18th Edition, New Delhi, Pages 2235 ; O P Ghai Essential Pediatrics, 6th Edition, Page 467