Mammogram: An X-ray of the breast that is taken with a device that compresses and flattens the breast. A mammogram can help a health professional decide whether a lump in the breast is a gland, a harmless cyst, or a tumor. A mammogram can cause pressure, discomfort, and some soreness that lasts for a little while after the procedure. If the mammogram result raises suspicions about cancer, a biopsy is usually the next step. The American Cancer Society and the American College of Surgeons currently recommend that a woman obtain her first, baseline, mammogram between the ages of 35 and 40. After the age of 40, a mammogram should be done yearly. Women who are at high risk for developing breast cancer may need to obtain mammograms earlier than these recommendations and at more frequent intervals.