This prospective study recorded the rate and potential for harm caused by errant medication orders at two teaching hospitals. Nearly 500 individual errors were captured with results reported per 100 patient-days and per 1000 medication orders. Pediatric patients younger than 2 years of age and intensive care unit patients experienced the highest rate of errors, whereas neonatal patients experienced the lowest rate. Incorrect dosage represented the most common type of error, with antibiotics most frequently involved. Although error rates occurred most in inexperienced physicians, no group was error free. The authors conclude that using specialized pharmacists to review every drug order can prevent medication errors and serious events.