A marking apparatus for the percutaneous placement of an imaging marker (12) at a predetermined location in a tissue mass to facilitate subsequent determination of the predetermined location, the marking apparatus comprising: a handle to be grasped by a user; a cannula (20) comprising: a peripheral wall forming a lumen (22), a proximal end carried by the handle, a distal end (24) terminating in a self-piercing tip (30), and a lateral opening (28) in the peripheral wall, which is open to the lumen; a plunger (40) having a distal end and slidably received within the lumen (22) for movement between a ready position where the distal end is spaced inwardly form the self-piercing tip (30) to form a marker recess in communication with the lateral opening (28) and sized to receive an imaging marker (12), and an expelled position, where the distal end is advanced a sufficient distance into the marker recess to expel a marker (12) contained therein through the lateral opening (28).