A tracheostomy tube assembly includes an outer tube (1) and an inner cannula (2) inserted in the outer tube. Two lugs (36) and (37) project outwardly from the inner cannula. The outer tube has a connector (15) that is rotatable and has catch members (28) and (29) that can be rotated into alignment with the lugs (36) and (37) on the inner cannula so as to retain the inner cannula in the outer tube. The inner cannula is removed by twisting the connector (15) through 90° so that the catch members (28) (and 29) move out of alignment with the lugs (36) and (37) to enable the inner cannula to be pulled rearwardly out of the outer tube.