A sliding door or window (1) comprises: a fixed frame (2); a sash (3) which slides horizontally and which has a perimeter groove (C); a pair of carriages (4, 4a) on which the sash (3) slides and which rest on a track (5); a controlling member (6) mounted on the sash (3), connected to operating means (7) which, when actuated by the controlling member (6), lift the sash (3) from the carriages (4, 4a) so that it can be slid open, and then lower the sash (3) when the sash (3) is returned to the closed position; a first slider (8) slidably fitted in the groove (C) made in an upper horizontal member (9) of the sash (3) and connected to the operating means (7); a first contact element (10) located in the proximity of the first slider (8) and rotatable between a lowered, non-operating position and a raised operating position; drive means (11) acting between the first slider (8) and the first contact element (10) and designed to allow a first position of lifting and stable positioning of the first contact element (10) when the sash (3) moves from the raised configuration to the lowered configuration in such a way as to prevent the sash (3) from being lifted off the fixed frame (2).