This study examined mammogram reports of women with Down syndrome (DS) treated in the largest medical facility specifically serving adults with DS in the United States. Records of 684 women and results of 993 mammograms were reviewed, including 902 screening and 93 diagnostic mammograms. Only 2 (0.7%) women had a diagnosis of breast cancer. This study found a low rate of breast cancer among women with DS, a finding which is consistent with previous studies. The financial cost per finding was high, the benefit of the mammograms questionable, and the potential for harm greater. With less than 1% of the women with DS in this study developing breast cancer, further discussion is recommended to assess whether mammography is a beneficial, cost-effective part of health maintenance for women with DS.