A mammogram is an X-ray image of your breast used to screen for breast cancer. Mammograms play a key role in early breast cancer detection and help decrease breast cancer deaths.During a mammogram, your breasts are compressed between two firm surfaces to spread out the breast tissue. Then an X-ray captures black-and-white images of your breasts that are displayed on a computer screen and examined by a doctor who looks for signs of cancer.A mammogram can be used either for screening or for diagnostic purposes. How often you should have a mammogram depends on your age and your risk of breast cancer.