A catheter assembly is disclosed. The catheter assembly comprise a hub assembly (4) comprising a hub (6) and a catheter (2) attached to the hub and a needle retracting device (5) releasably attached to hub assembly which is arranged to project a needle (3) through the catheter to allow catheterization and, in response to user actuation, to retract the needle and to be detached or to allow detachment from the hub assembly. The needle retaining device comprises a chassis (20) extending along an axis from a base (24) and a slider (21) carrying the needle supported on the chassis, arranged to be moveable away from the base along the axis from a first position in which the needle projects through the catheter to a second position in which the needle is withdrawn from the catheter and is shielded by the chassis. The chassis and hub comprise movable locking members (29 Fig. 8) and cooperating locking surfaces (17 Fig. 6) for engaging the locking members and wherein the slider comprises retaining surfaces (52) for limiting movement of the locking members. The catheter assembly is configured such that, when the slider is in the first position, the locking members are discouraged or prevented from disengaging from the locking surfaces by the retaining surfaces and, when the slider is in the second position, the locking members are free to disengage from the locking surfaces and so allow the needle retracting device to disengage from the hub assembly.
