An apparatus for deflecting a catheter or lead, for example a deflectable stylet or guidewire. The device includes an outer tubular member, a tension member mounted within the outer tubular member and coupled to the outer member and a handle mounted at the proximal end of the tubular member. The handle includes a major handle portion which has a rotatable knob located at its distal end, surrounding a proximal portion of the outer tubular member and provided with inwardly directed threading and an inner slider member provided with outwardly directed threading engaging the inwardly directed threading of the knob. The slider is advanced or retracted longitudinally within the handle by rotation of the knob but is rotationally fixed with regard to the major handle portion. The outer tubular member is engaged at its proximal end with the inner slider member and the tension wire is fixedly engaged with the major handle portion, whereby rotation of the knob results in advancement or retraction of the outer tubular member relative to the tension wire and the major portion of the handle, which in turn causes the deflection of the outer tubular member.