A surgical trocar includes an operative sleeve adapted for disposition across a tissue barrier and an obturator removably disposed in the sleeve. An obturator includes a cutting element which is operable to cut the tissue. The obturator and the operative sleeve can be advanced through the cut tissue and the obturator removed leaving the sleeve operatively disposed for further surgery. A cutoff and reset mechanism is responsive to a condition present when the obturator penetrates the tissue barrier to inhibit further cutting by the cutting element. A reset mechanism is manually operable through the conscious efforts of the surgeon to reset the trocar should further cutting be desired. The cutoff and reset mechanisms can be embodied mechanically as well as electrically and adapted to both mechanical and electrosurgical trocars.