The invention relates to a regulation mechanism for built-in sliding doors of the type comprising a sliding leaf (4), a guide (6) in the lower part of said sliding leaf (4) and a fixed stop (16) inside said guide (6), comprising a cover (1) fixed at the end of the sliding leaf (4), a mobile stop (2) slidable through the inner part of the guide (6) situated between the cover (1) and the fixed stop (16), and an adjustment screw (3) traversing the cover (1) and the mobile stop (2) by means of which the relative position between both elements (1) and (2) is regulated.