Many functions important to realizing the full potential from electronic health records (EHRs) may not be selected by all physicians using EHRs in the ambulatory setting. This article examines the extent to which EHR systems used by Florida physicians include functionalities that the Institute of Medicine has designated as being critical for optimal performance. Results indicate that EHR systems used by recent adopters, when compared with early adopters, appear to be missing key patient safety and cost control functions. Overall, many physicians are only partially adopting EHR technologies, suggesting that published adoption rates may be exaggerating the true rate of diffusion. Copyright © 2007 by the American College of Medical Quality.