A localization needle assembly includes an outer tubular cannula and an inner needle slidably mounted for movement within the outer cannula between extended and retracted portions, the needle having a pointed tip which projects from the front end of the assembly when the needle is extended while the surgeon locates a lesion. When the tip is retracted, a barb, which is secured to the needle, is deployed through an opening in the sidewall of the outer cannula when the needle is retracted, the barb anchoring the needle assembly in body tissue in the proximity of the lesion. Detachable handles are provided for locking the inner needle and outer cannula together and to facilitate extension and retraction of the needle. In one embodiment, the outer cannula has a helical screw tip for securing the needle assembly to a body organ or body tissue. A guide assembly is advanced along the needle assembly which has been inserted into the body tissue to locate a lesion to position one end of a guide wire at the lesion to facilitate the introduction of a surgical instrument into the body and guidance of same directly to the lesion.