A sliding door or window (1) comprises: a fixed frame (2); a sash (3) that opens and closes by sliding horizontally relative to the fixed frame (2); a sliding unit or carriage (4) associated with the bottom horizontal member (3a) of the sash (3) and resting on a horizontal base track (5); a controlling member (6) located on the sash (3) and connected to operating means (7) which, when actuated by the controlling member element (6), lift the sash (3) from the carriage (4) and lower the sash (3) through drive means (8) located between the sash (3) and the carriage (4) and connected to the operating means (7); closing means (9) acting between the vertical member (3b) of the sash (3) and the vertical member (2b) of the fixed frame (2) which, in the closed configuration, abut against each other edge to edge; the operating means (7) comprise a first rod segment (7a) and a second rod segment (7b) slidable in both directions in respective grooves (3c) formed on the profile of the vertical member (3b) and the upper horizontal member (3d) of the sash (3), respectively, and connected to each other by first right-angle drive means (10); the two rod segments (7a, 7b) operate on respective closing means (9, 9a) in such a way as to enable multiple and simultaneous closure of the sash (3) by a single direct movement of the segments (7a, 7b) using the controlling member 6).