^It's actually more common than one might imagine, though I think it more often happens that males are misidentified as females. There is even a community (I believe in South America, though I'm not positive because it's been a while since I studied this), where it is actually very common for boys to be raised as girls until they hit puberty, their testes descend and their penises grow. It's genetic and the community is tight knit, so it happens frequently there. Sometimes people refer to this as "ambiguous genitalia" but I know that many individuals who have genitalia not as easily classified as male or female find that term offensive.
I'd highly, highly recommend the novel Middlesex
by Jeffrey Eugenides, which is told from the perspective of an intersex man raised as a girl. It's one of my favorite novels, actually.