Screening mammography, breast x-ray examination of women without any symptoms or signs of breast cancer, is a safe and efficacious procedure. Modern mammography, which is a low-dose radiographic examination, allows safe and correct diagnosis of about 90% of the cancers. Occult breast cancers, those found only with screening mammography, have a much lower rate of axillary node metastases and a much better prognosis, when compared with palpable breast cancers. With screening mammography, minimal breast cancers that are early in their development and have a remarkably improved prognosis can often be detected also. It is generally agreed that women with minimal cancers do not require mastectomies.