A cavity (3) such as the urethra of a patient is lined by providing a lining device that comprises an eversible chamber (12) and a liner (16) connected thereto. Fluid pressure is applied to the chamber (12) to cause the chamber (12) to evert and advance into the cavity (3) such that the chamber (12) carries the liner (16) into the cavity. A vacuum is then applied to the chamber (12) to cause it to deflate. A part, such as a catheter or cable, can then be inserted into the cavity through the liner (16). If the cavity is the urethra of a patient, the liner shields the catheter from the distal part (1) of the urethra which is colonised with bacteria, and therefore reduces the risk of a urinary tract infection.
