A new technique of cystoscopic insertion of laser fiber into the prostate is described for interstitial laser thermal therapy in the treatment of benign prostatic hyperplasia. The technique uses the inherent physical properties of the fused silica laser fiber with the assistance of a standard cystoscope to insert the laser fiber into the inner region of the prostate gland. Laser thermal therapy is subsequently maintained within the inner prostate at a distance from the prostatic urothelium. The technique described is simple, safe, and minimizes the potential for thermal injury to the prostatic urothelium.