The National Quality Forum has designated computerized physician order entry (CPOE)-the electronic entry of physicians' orders into a clinical computer system for patient care-as 1 of their 30 Safe Practices for Better Healthcare in 2003. Since that time, the body of knowledge and experience with CPOE has grown considerably. This article reexamines the objectives, requirements for achieving these objectives, and evidence of efficacy for this practice, and evaluates new published studies in CPOE. It reviews relevant issues of medication safety, the likely impact of CPOE, the efficacy of CPOE in various studies, key measures of impact of the practice, and important implementation issues. Although it is clear that CPOE can cause errors as well as prevent them, the evidence clearly suggests that CPOE reduces the rates of medication errors and serious medication errors, although studies with adequate power to assess the impact of CPOE on the preventable adverse drug event rate have not been performed. Finally, updates and revisions to the current National Quality Forum CPOE practice standard and implementation examples are suggested.