Gender Identity in 5 yr old girl

[kimettari]

I am concerned about my 5 yr old adopted daughter and her continued desire to dress and act like a boy.  She also wants to be called a boy name instead of her own.  She has an older brother who is 7.  It seems to have progressed well beyond what I would consider normal tomboyish behavior.  She wants to buy boy clothes and requested a short haircut that looked more masculine.  She will only play with boy toys (Star Wars, trains, etc.) although she doesn't appear to even enjoy playing with them.  She will only play with boys at school (kindergarten) as well.  She also has adopted boy mannerisms like wearing her hats backwards, standing with her hands in her pockets, wanting to wear thick masculine chains for necklaces, etc.  This has been going on about a year or so and her father and I dismissed it initially and have pretty much let her dress the way she's wanted within limits.  We have begun to wonder if there is anything we should be doing to either address it or just let it run it's course.  Please advise!