The potential of health information technology (IT) to transform health care delivery has spurred health IT adoption and will likely contribute to increased investments in coming years. Although an extensive literature shows the value of health IT at leading academic institutions, its broader value remains unknown. We sought to estimate IT's effect on key patient safety measures in a national sample. Using four years of Medicare inpatient data, we found that electronic medical records have a small, positive effect on patient safety. Although these results are encouraging, we suggest that investment in health IT should be accompanied by investment in the evidence base needed to evaluate it.