An anti-condensation arrangement (5) for catheters comprising a heated air generator (6), a sheath (9) covering a catheter (4) such as to create a cavity (I) with it, and a device (7,8) for the input of heated air produced by the generator (6) into the cavity (I). The sheath (9) has a venting opening (9b) to allow the exit of heated air from the cavity (I) and therefore continuous exchange of air.