The invention relates to a radial piston machine and a piston for a radial piston machine, wherein pistons that are movable in the radial direction are guided along a lifting surface of a cam ring by way of a roller. The roller is hydrostatically supported by way of a pressure groove in a sliding bearing surface of a roller cage. The geometry of the pressure groove is selected such that both the leakage is reduced and the lateral support is improved by enlarging hydrostatic and hydrodynamic surface sections.