Electronic prescribing (E-RX) is a component of the Medicare Prescription Drug, Improvement, and Modernization Act of 2003 (MMA). The objective of this study was to identify factors related to physicians' adoption of E-RX for outpatients. This study employed an electronic survey of US physicians who subscribe to the Physicians Online Internet service. Electronic prescribers were compared to traditional prescribers in terms of demographics, practice type and location, technology use, and beliefs about E-RX. A total of 1104 physicians responded, 19% of whom prescribed electronically. Electronic prescribers were more likely to be generalists practicing in academic or publicly funded centers, have fewer years in practice, and work in technology-equipped offices. They also held different beliefs versus traditional prescribers in terms of E-RX limitations and its potential to improve medication safety and prescribing efficiency. In addition to financial incentives established by MMA, adoption can be stimulated by improvements in the technology and on organizational commitment.