Mammography and breast ultrasound are two of the most common and useful tests used in breast surgery. When we prescribe breast ultrasound and mammography to patients in the clinic, one of the most frequently asked questions is: Which is better, ultrasound or mammography? Which one is clearer? Is it enough to do one of these tests? In fact, ultrasound and mammography are two completely different examinations; ultrasound has its own advantages in evaluating the local microstructure and mammography has its own advantages in screening breast cancer, and they can complement each other in many aspects. For example, mammography is more sensitive to calcified foci, while ultrasound has a unique advantage in the diagnosis of cysts. Below I will detail the features and differences between these two tests. I. Mammography The use of mammography was a landmark event in breast surgery. Due to the widespread use of mammography, a large number of early breast cancers without clinical symptoms have been detected earlier, and the death rate of breast cancer population has been greatly reduced as a result. Mammography is uniquely suited for early-stage breast cancers, especially those without masses, which appear on mammography only as calcified spots or distorted local structures. In clinical practice, mammography is an important tool for breast cancer screening, and annual mammography is recommended for women over 35 years of age. The age of screening should be advanced for patients with a family history of breast cancer. For patients with confirmed or suspected breast cancer, mammography of both breasts can help detect multiple or bilateral breast cancers. Regular mammograms are also needed after treatment for benign and malignant disease. Mammography can also be used to localize biopsies of lesions that do not have clinical masses (such as calcified foci). Under mammography surveillance, a localization guide wire is placed near the lesion and the lesion is accurately removed intraoperatively according to the position of the guide wire, reducing trauma while improving diagnostic accuracy. The radiation dose of mammography is very low, and the cancer rate for adult women is similar to the natural incidence rate. For women under the age of 35, mammography is generally not recommended if they are not at high risk for breast cancer because of the dense breast tissue. Ultrasound of the breast Compared with mammography, ultrasound has no radiation damage and is suitable for any population, especially young women and women during pregnancy, and can be performed multiple times. Ultrasound has a unique advantage in the diagnosis of breast cysts. Examination of the axillary and supraclavicular lymph nodes is also a strong point of ultrasound. An experienced ultrasonographer is able to detect those tiny tumors that are not reachable. Puncture localization or biopsy of microscopic lesions under ultrasound guidance has become an important tool in breast surgical biopsy, greatly improving accuracy and reducing the number of open surgeries, while many such lesions do not show or do not show up on mammograms. Currently, many studies have shown that because Asian women have dense breast tissue and the age of onset of breast cancer is earlier than that of Westerners (the peak incidence of breast cancer in Europe and the United States is after menopause, the breast tissue is atrophic and thin, and lesions are more clearly shown on mammography; while the peak incidence of breast cancer in Asians is before menopause, at the age of 40-45, the breast tissue is dense and lesions are less well shown on mammography), B ultrasound is becoming more and more important in breast cancer screening and diagnosis. The role of ultrasound in breast cancer screening and diagnosis is becoming more and more important. It is also important to emphasize that due to its operational characteristics, ultrasound results are highly dependent on the machine and the doctor’s experience, and there is a certain rate of missing and misdiagnosis (in fact, this is true for any examination), which is normal. Therefore, we should not be superstitious about the examination, but should combine the physical examination and these auxiliary examinations for comprehensive evaluation, and also need regular review and follow-up. Only in this way can we improve the diagnosis rate of early breast cancer and, thus, further improve our treatment outcome and patient prognosis.