Abstract: Concretions, such as kidney stones, are nonsurgically fragmented by apparatus which produces focused shock waves. A truncated ellipsoidal reflector is positioned against the patient such that one focus thereof is coincident with the concretion. The reflector is filled with a liquid medium having an acoustical impedance similar to living tissue. A laser beam is focused at the remaining focus, thereby producing a shock wave which is coupled through the liquid medium and the patient's tissue and focused at the concretion. By controlling the energy level and duration of the laser beam, a fragmenting tensile stress is imparted to the concretion.