Abstract: A hydraulic booster for slip-controlled brake systems, including a booster piston (1) arranged in a booster housing (11) and confining a booster chamber (4). A braking pressure control valve is provided whose control part (12) is actuatable by a lever mechanism (13) as a function of the piston of the control part (12). An actuating piston (2) is displaceably guided in the booster piston (1) and is positioned by way of a push rod which cooperates with the lever mechanism (13). To provide a hydraulic booster to realize boosting factors of any desired size, both of constructional and strength-minimizing nature, an annular surface (24) is formed the stepped actuating piston (2), on the side of the push rod (22) and is larger than the total area of any opposing annular surfaces, subject to the booster chamber pressure to create a net force acting to oppose the push rod force and allow setting of the boosting factor by adjustment of the area of the annular surface.