Set Smooth problem

Hi all, i was modeling a mannequin to do some simple animations as an attempt to learn/get better at it. Anyways i was modeling it just now and i finished up the bulk of it, hit set smooth, and a bunch of the faces turned into shades of black/grey. To try and fix it i deleted the darkened faces and just re-filled them. That strategy worked but i still am tempted to ask how this happened and if there is a simpler solution.

thanks for any help

Select all and recalculate normals(Ctrl-N). Some of the normals are facing inward.

It could also be that you are getting odd smoothing from faces at acute angles. You could also try adding an Edge Split modifier through the editing panel.

ahh, thank you very much.