In medical or dental handpiece having a treatment tool driven by means of a drive part via a transmission arrangement, the transmission arrangement contains at least two planetary transmission stages connected one after another, which each have a sun gear mounted on a drive shaft, a planetary gear carrier having a plurality of uniformly distributed planetary gears cooperating with the sun gear, and a hollow gear, fixed to a housing, surrounding the planetary gears, having an inner toothing, wherein the planetary gear carrier of at least one transmission stage serves as drive shaft and carrier of the sun gear of the following transmission stage. In order to increase the stability of the arrangement the drive shaft for each transmission stage is extended beyond the sun gear driven thereby and in that the planetary gear carrier belonging to this sun gear is arranged rotatably on the extension.