This is really not a masculine name, but a nickname for a girl named Vilhelmiina, Vilma or other names beginning with "Vil" or "Wil" (just like slight night shiver said).
-- Anonymous User 6/27/2009
Officially, this is a masculine name. It's not common, so I wouldn't be surprised to hear it used as a girl's nickname, but I'd expect it to be hard to pass it officially as a girl's name, since, according to the statistics from the Finnish Population Register Centre, it's always been exclusively masculine.