The assessment of MDRO infection and colonization should include the identification of known carriers, the detection of hospital-specific and healthcare-associated acquisition, an estimation of the burden of serious infection, an understanding of the reservoir affecting the transmission of MDROs, and an evaluation of the effect of intervention. Several strategies can be used to obtain data that aid in this assessment. We have defined and categorized the recommended metrics for each of these aspects of measuring MDRO infection and colonization, for use by healthcare facilities. © 2008 by The Society for Healthcare Epidemiology of America. All rights reserved.