A tracheostomy tube assembly includes a flexible tube (1, 1′) and a flexible introducer (2, 2′) within the tube, the introducer having a passage (22) along its length for receiving a guidewire (9) inserted into the trachea (7) through a tracheostomy (6). The tube (1) has an inwardly-projecting collar (17, 17′) at its patient end (11), which engages an outwardly-projecting shoulder (24, 24′) on the introducer (2, 2′) so that the tube does not ride rearwardly along the introducer during insertion. The flexibility of the assembly is such that it can be inserted through the tracheostomy (6) while straight and then curves to follow the guidewire (9) as its patient end enters the trachea (7).