A system for delivering a probe into a body part to perform a therapeutic or diagnostic procedure therein which includes an elongated probe device which is disposed within a protective sheath and which has a rotary drive unit connected to its proximal extremity to rotate the probe about its longitudinal axis, preferably at a rate above 50 rpms while applying axial pressure thereto to cause the distal end of the probe to penetrate through the patient's tissue to a desired location in the body part where the procedure is to occur. In a presently preferred embodiment, the probe is an optical fiber which is delivered into a male patient's prostate gland through the patient's prostatic urethral wall. The optical fiber is optically connected to a source for laser energy (815 nm) which is emitted from the distal end of the optical fiber to ablate prostatic tissue surrounding the distal end. A sheath is disposed about the optical fiber to support the shaft thereof and to minimize damage to the working channel of a cystoscope through which the device is usually advanced to reach the desired location within the patient's prostatic urethra.