The invention relates to a master cylinder (1), especially for a regulated brake system. Said master cylinder comprises at least one piston (3,4;53,54) that can be displaced in a housing (2) and is sealed, by means of a sealing element (5,6) arranged in an annular groove (23,24) of the housing (2), from a pressurised region (7,8) that can be connected to a pressureless wake region (11,12) by means of transversal boreholes (9,10;50,51) in the piston (3,4;53,54). The invention is based on the fact that the inner side (13,14;59,60) of the piston (3,4; 53,54) is provided with recesses (15,16,17) in which the transversal boreholes (9,10;50,51) end.