Cutting insert with twisted relief surface

A cutting insert, preferably for milling cutters, comprises an upper side or chip surface, a bottom surface and side surfaces extending between the upper and bottom surfaces. At least one of the side surfaces having a relief surface adjacent to a cutting edge, which relief surface is helically twisted along the cutting edge so that the relief or clearance angle decreases with increasing cutting depth. This arrangement makes it possible to obtain an equally large clearance along the cutting edge even with a negative inclination of the cutting insert in the milling cutter body.