As a result of health education programs that have stressed self-examination and the importance of early diagnosis and treatment, less than 5 percent of breast lesions seen in clinical practice today are malignant. Nevertheless, breast cancer is the leading cause of deaths due to cancer in women and the second most common breast lesion. Chronic cystic mastitis, the most common breast lesion seen in women, can often be treated conservatively by aspirating the cystic fluid. Close follow-up is necessary so that if carcinoma develops, it can be treated early. Carcinoma is unpredictable but not hopeless. Although controversy exists regarding treatment, radical mastectomy is still the preferred treatment in most cases. Other breast diseases include adenofibroma, a common lesion requiring excisional biopsy for positive diagnosis; nipple discharge, which should be carefully examined cytologically; and relatively rare breast lesions, including intraductal papilloma, adenosis, traumatic fat necrosis, and cystosarcoma phylloides.