A localization needle assembly includes an outer tubular cannula and a reinforced needle structure slidably mounted for movement within the outer cannula between extended and retracted portions, the needle structure defining a rearwardly extending barb which is contained within the outer cannula when the inner needle is extended while the surgeon locates a lesion. When the inner needle is retracted, the barb is deployed through an opening in the sidewall of the outer cannula for anchoring the localization needle assembly in body tissue in the proximity of the lesion.