Mammograms of 81 patients who received radiation therapy to the breast were analyzed for patterns of pre- and postirradiation calcifications. Malignant calcifications may remain stable, diminish, or completely disappear following irradiation. The persistence of calcifications need not indicate residual cancer. Calcifications can develop following irradiation which are similar to either intraductal or secretory calcifications. Unusual calcifications may develop at the site of an irradiated cancer. It is important to recognize that benign calcifications can develop so that they will not be confused with recurrent malignancy.