Occasionally, a breast lesion is visible in only one mammographic projection. A simplified method of using parallax in a dedicated mammographic system has been devised to locate accurately lesions that are not visible in two orthogonal projections. In eight patients, a parallax approach from essentially a single mammographic position was used to place a hookwire preoperatively at nonpalpable suspicious abnormalities detected by mammography. Needles were inserted parallel to the chest wall while the breast was compressed in the mammographic unit. In each case, the tissue containing the lesion was pierced by a needle chosen to be longer than the distance from the skin to the abnormality. Simple geometric ratios were used to determine the position of the lesion along the needle shaft after slightly changing the mammographic projection and viewing the needle obliquely. In all cases, this parallax approach permitted accurate localization of the lesion.