A transurethral needle ablation device for use with the human hand for radio frequency ablation of a target volume in the tissue of a prostate of a human male having a bladder with a base and a penis with a urethra therein formed by a urethral wall extending into the base of the bladder along a longitudinal axis with the tissue of the prostate surrounding the urethra near the base of the bladder. The device comprises a bridge having proximal and distal extremities and having a passage therein extending from the proximal extremity to the distal extremity. A sheath having proximal and distal extremities is secured to the bridge and has a passageway therein in communication with the passage in the bridge. The sheath is sized so that it can enter the urethra and has a length so that when its distal extremity is in the vicinity of the prostate, the proximal extremity is outside the urethra. A disposable needle assembly having proximal and distal extremities is removably mounted in the passage in the bridge and extends through the passageway in the sheath. The needle assembly includes at least one needle electrode and an insulating sleeve coaxially disposed on the needle electrode. The proximal extremity of the needle assembly is caused to be moved sideways at an angle with respect to the longitudinal axis to face the urethral wall. A mechanism is carried by the proximal extremity of the needle assembly and the bridge for causing advancement of the needle electrode and the insulation sleeve thereon through the urethral wall and into the target volume in the tissue of the prostate with a portion of the electrode being free of the insulation but with the insulation extending through the urethral wall.