The commonest cause of primary Amenorrhoea is:

Most common cause of Primary Amenorrhea = Gonadal dysgenesis/ovarian dysgenesis 2nd most common cause of Primary Amenorrhea = Mullerian agenesis (Mayer Rokitansky Kuster Hauser Syndrome)  “Mullerian agenesis is a relatively common cause of primary amenorrhea, more frequent than congenital androgen insensitivity and second only to gonadal dysgenesis”  3rd most common cause is testicular feminizing syndrome.