A tracheostomy tube assembly includes an outer tube (1) and an inner cannula (2) removably inserted in the outer tube. The connector (15) on the machine end of the outer tube is rotatable through about a quarter turn and has a screw thread (30) on its inner surface. The hub (33) on the machine end of the inner cannula (2) is also formed with a screw thread (35) arranged to engage with the screw thread (30) in the connector. The inner cannula (2) is pulled into the outer tube (1), or is pushed outwardly of the tube, by rotating the connector.