Abstract: A trocar system comprises a trocar housing, a pointed stylet arranged so that the pointed tip can be selectively extended outwardly (distally) from the trocar housing, a return spring in the trocar housing for retracting the stylet into the housing and a piston and piston latch system disposed within the trocar housing for restraining the stylet from retracting. The piston includes a cam element for de-latching the piston from its latched position to allow the return spring to retract the piston into the housing. The stylet engages the piston in a slot to permit limited longitudinal movement of the stylet into the housing. A distally-biased element which carries an engaging pin and is forced to move proximally by the tissue resistance experienced as the trocar is forced to puncture a body cavity wall, automatically moves to its original distal location after the tip of the trocar has completely passed through the wall.