a trocar assembly consisting of a trocar tube subassembly and a separate interengageable trocar body subassembly is provided . the trocar body subassembly includes an elongated obturator having a sharp pointed tip which is normally housed within an elongated tube of the trocar tube subassembly . the obturator is extendable from a retracted position within the tube wherein the tip is recessed from the tube end to an operative position forward of said tube end and outside the tube . by manually advancing the trocar assembly against a body wall , the resisting force locks the obturator in the operative position . relaxation of the force incident to passing through the body wall causes the obturator to be automatically unlocked and retracted to its initial position with the tip positioned protectively within the tube , thereby protecting body tissues and organs from being damaged by the tip when it enters a body cavity beyond the wall .