I just finished a kit I purchased a few years ago, but did not pre-wash the fabrics. Generally though, I pre-wash all my fabric yardage and fat quarters, but not the smaller precuts. I have in the past but the precuts can be messy and tangled, so I don't pre-wash them, but I admit I seldom use precuts, mainly yardage and fat quarters. I've found that all fabrics do not shrink the same (even if it's very minimal shrinkage), and I want to know that before I make the quilt.