Computerized provider order entry (CPOE) clearly prevents medication prescribing errors in the inpatient setting, but its effect in primary care has been less well studied. This systematic review identified 10 randomized controlled trials of information technology-based approaches to preventing medication errors in primary care. Results were mixed, with only CPOE combined with decision support and pharmacist-led interventions yielding positive results. Superior performance of CPOE in primary care will be necessary to demonstrate an adequate return on investment for this technology.