Windows itself perhaps, but not the Windows API. If you've ever done any low-level Windows development, it's pure C.

See here for a tutorial using it for basic GUI stuff:

http://zetcode.com/gui/winapi/firststeps/

I've even seen several games that use it directly for keyboard handling and such to this day. And all the new, fancy GUI frameworks which exist on Windows are basically just wrappers on top of WinAPI.