A delivery system (50) for a detachable medical device (10) comprises a first helical wire (12) attached to the medical device, a second helical wire (18) attached to a deployment member (16) and a wire coil (30) which is arranged to interconnect the helical wires (12, 18). A pull on a release wire (32) at one end of the coil (30) detaches the coil from at least one of the helical wires whereby to detach the medical device (10) from the deployment member (16). In a modification a release coil (130) is arranged between concentric helical wires (112, 118).
