The subject of the invention is a disc brake with automatic adjustment of the type incorporating a caliper (10) mounted to slide on a fixed support by way of at least one axial pin, a brake motor (34) acting directly on a first friction element (26) and as a result of reaction via the caliper (10) on a second friction element (30). The brake motor (34) incorporates a mechanical control (48, 50, 54) acting on a hydraulic control piston (36) via an automatic-adjustment device. The automatic-adjustment device is formed by a screw (68) -and-nut (88) system of reversible pitch, which is actuated by the piston (36) beyond a predetermined stroke of the latter. According to the invention, a monitoring piston (80) immobilizes a sleeve (114) fixed in rotation to the nut (88), when the hydraulic control pressure reaches a predetermined value. The invention is used for the braking of motor vehicles.