In the Netherlands, where doctors keep such records, they calculated in 1993 that 1 in 11,900 persons born male and 1 in 30,400 persons born female had taken hormones to change sex.
First person to guess the primary reason this struck me as significant/unexpected gets a prize. I'm not sure what the prize will be – sketch, ficlet, something in the mail – but you'll get one.
(And hell, I'll give one for the first on Dreamwidth and one for the first on LiveJournal. Why not?)