Abstract: Relief of urethral obstruction is achieved by heat ablation of prostatic tissue by an ablation instrument passed within the urethra to a position in the prostate near the point of urethral obstruction. An electrode is coupled to a high-frequency power supply to ablatively heat the urethra and the prostatic tissue near the urethra. Guidance of the electrode placement may be monitored by an imaging device. The instrument may consist of a catheter with an inflatable balloon structure for positioning the instrument. The temperature of the tissue may be sensed at the electrode to control the high-frequency heating energy and ablation process.