Abstract: A torque-transmitting structure such as a guidewire or catheter is formed of a generally flat band or wire twisted so that its longitudinal edge generally forms a helix. This twisted helical portion may be attached to a proximal shaft, and a tip member may be attached to the distal end of the helical portion. In some embodiments, the device is made of a single piece of wire, and in some embodiments, a spring coil may cover the helical portion. Where the device is a fixed wire balloon catheter, the helical portion may be attached to a proximal shaft, and the balloon mounted on the helical twisted wire, a plastic sheath encasing the main shaft and wire up to the balloon for inflation of the balloon. The helical guidewire may also be used in an over-the-wire balloon catheter.