Chibi!Italy is a boy, but everybody thinks that he is a girl. There is a comic strip later on where Italy's voice matures so that he sounds like a guy (or at least closer to it xD) and Austria and Hungary are surprised.

http://community.livejournal.com/hetalia/101125.html


There are also a few webcomics where it looks like HRE thinks Chibi!Italy is a girl.

http://community.livejournal.com/hetalia/64747.html
http://community.livejournal.com/hetalia/98987.html

So yeah. Chibi!Italy is a boy, it's just that since his voice was girly, looked girly and he was always dressed in dresses or maid outfits (because of his voice/looks), people thought he was a girl. x'D