Abstract: The present invention entails a method and apparatus for balancing a high speed rotary tool assembly. A pair of closed balancing rings are journalled about a cylindrical bearing surface formed around a rotary tool holder with each ring being rotatively mounted about the bearing surface independently of each other. The tool holder is adapted to receive and hold a cutting tool. After determining the unbalance of the tool holder and cutting tool, the rings are rotatively adjusted about the bearing surface to create an unbalance within the tool rings and the position of the tool rings is adjusted such that the created unbalance of the tool rings is disposed opposite the determined unbalance of the rotary tool holder and cutting tool.