A disposable sheath is provided for a radiofrequency ablation device which includes both an ultrasonic imaging probe and a detachable needle advancement assembly. The sheath includes a distal region which conforms closely to a shaft of the ultrasonic imaging probe but drapes more loosely over a handle of the ultrasonic imaging probe. The disposable sheath allows attachment features on both the ultrasonic imaging probe and the needle advancement assembly to be easily visualized and easily connected together.
