Never knew it could be a girl's name. I love this beautiful name for a boy, but the problem is that in Denmark it is more than overused. I know so many people named Kristian or Christian, among them my brother, who I call Krisjang. And now we just had a new Danish prince named Christian so I'm afraid it will keep being that popular.
Girl name?! Wow! I never never NEVER heard this name for a girl. A lot of my friends have the name Kristian but hey, a girl? I just can believe that! I just saw that it is ONE girl in Sweden who has the name Kristian, poor girl. [noted -ed]
Earthnut, please do not contribute information about usage in Slovenia for the names that are very rare there. Slovenes want to be fancy and they think it's better to give to a baby a name which is easier to pronounce for foreigners. So originally, Kristian isn't a Slovene name.