A thrust reversal device for a turbojet engine nacelle is provided that includes a deflection means and at least one cowl moveable relative to at least one fixed structure including at least one at least partly peripheral front frame and equipped with means for connection to a corresponding upstream portion. The front frame has a deflection edge having an upstream extension forming a deformable flap intended to become an aerodynamic interface with the corresponding upstream portion to which is attached the front frame, and in that a portion of the moveable cowl is conformed so as to, in the closing position, interface with said upstream attachment portion by forcing withdrawal of the deformable flap.