We describe the development, design, fabrication, and testing of an optical wire to assist in the surgical removal of small lesions during breast-conserving surgery. We modify a standard localization wire by adding a 200-μm optical fiber alongside it; the resulting optical wire fit through an 18 gauge needle for insertion in the breast. The optical wire is anchored in the lesion by a radiologist under ultrasonic and mammographic guidance. At surgery, the tip is illuminated with an eye-safe, red, HeNe laser, and the resulting glowball of light in the breast tissue surrounds the lesion. The surgeon readily visualizes the glowball in the operating room. This glowball provides sufficient feedback to the surgeon that it is used (1) to find the lesion and (2) as a guide during resection. Light-guided lumpectomy is a simple enhancement to traditional wire localization that could improve the current standard of care for surgical treatment of small, nonpalpable breast lesions.