PURPOSE: To prospectively determine the diagnostic accuracy of optical absorption imaging in patients with Breast Imaging Reporting and Data System (BI-RADS) 3-5 breast lesions. MATERIALS AND METHODS: Forty-six patients with BI-RADS classification 3 (11%), 4 (44%) or 5 (44%) lesions, underwent a novel optical imaging examination using red light to illuminate the breast. Pressure was applied on the breast, and time-dependent curves of light absorption were recorded. Curves that consistently increased or decreased over time were classified as suspicious for malignancy. All patients underwent a core or surgical biopsy. RESULTS: Optical mammography showed a statistical difference in numbers of suspect pixels between benign (N=12) and malignant (N=35) lesions (respectively 1325 vs. 3170, P=0.002). In this population, optical imaging had a sensitivity of 74%, specificity of 92%, and diagnostic accuracy of 79%. The optical signal did not vary according to any other parameter including breast size or density, age, hormonal status or histological type of lesions. CONCLUSION: Optical imaging is a low-cost, non-invasive technique, yielding physiological information dependent on breast blood volume and oxygenation. It appears to have a good potential for discriminating benign from malignant lesions. Further studies are warranted to define its potential role in breast cancer imaging.