This study, one of the first to analyze prescribing errors in community primary care practices, found a remarkably high rate of errors. Nearly one in four prescriptions contained at least one error in dosing, frequency, or patient instructions, and a startling proportion of prescriptions had illegibility errors as well. Computerized provider order entry (CPOE) could have prevented a large proportion of these errors, and recent studies have shown that CPOE can decrease prescribing errors in community-based office practices. A Patient Safety Primer discusses outpatient medication prescribing errors and other pressing safety issues in outpatient practice.