A male with azoospermia. On examination size of testis normal FSH normal testosterone normal. Most probable cause is: (A) MAL descended testis, (B) Klinefelter's syndrome, (C) Kallmann's syndrome, (D) VAS obstruction
Answer is D. A normal level of FSH in azoospermia suggests an obstructive lesion in the vas or epididymis. 
High FSH may indicate primary gonadal failure.