A prescription monitoring system was established in our pediatric outpatient clinic. The system was used to monitor prescriptions written by members of our pediatric housestaff and faculty. A total of 884 consecutive prescriptions written during a six-week period were reviewed for the presence of the components of a complete prescription as well as certain prescribing errors. Numerous prescription writing errors were identified. Errors were especially common in prescriptions for controlled substances. The number and types of errors raise important questions about the quality of prescriptions written in our clinic and about the cost of these errors in terms of patient, physician, or pharmacist time as well as drug cost and potential therapeutic mishaps.