Hospitalized children are particularly vulnerable to serious medication errors, as many pediatric medications must be dosed individually according to weight. Tenfold dosing errors, where children receive doses an order of magnitude different than appropriate, have resulted in patient harm in the outpatient setting, and this study found that more than 250 such errors occurred over a 5-year period at a tertiary care children's hospital. Although pharmacists intercepted nearly half the errors, more than one-third occurred at the time of medication administration and therefore would not have been prevented either by pharmacists or by computerized provider order entry.