OBJECTIVE: To quantify the type and frequency of drug administration errors to pediatric in-patients and to identify associated factors. DESIGN: Prospective direct-observation study of drug administration errors from April 2002 to March 2003. SETTING: Four clinical units in a pediatric teaching hospital. STUDY PARTICIPANTS: Twelve observers accompanied nurses giving medications and witnessed the preparation and administration of all drugs to all patients on all weekday mornings. INTERVENTION: None MAIN OUTCOME MEASURE: Discrepancies between physicians’ orders and actual drug administration. RESULTS: During the 1719 observed administrations to 336 patients by 485 nurses, 538 administration errors were detected, involving timing (36%), route (19%), dosage (15%), unordered drug (10%), or form (8% form). These errors occurred for 467 (27%) of the 1719 administrations. Intravenous drugs (OR=0.28; CI=0.16–0.49; versus miscellaneous) were associated with fewer errors. Error rates were higher for cardiovascular (OR=3.38; CI=1.24–9.27; versus miscellaneous) and central nervous system drugs (OR=2.65; CI=1.06–6.59; versus miscellaneous); unspecified dispensing system (OR=2.06; CI=1.29–3.29; versus store in the unit); nonintravenous nonoral administration (OR=4.44; CI=1.81–10.88; versus oral administration); preparation by the pharmacy (OR=1.66; CI=1.10–2.51); and administration by a hospital pool nurse, temporary staffing agency nurse, or nurse intern (OR=1.67; CI=1.04–2.68; versus registered full-time nurse). Each additional management procedure in the patient increased the risk of error (OR=1.22; CI=1.01–1.48). CONCLUSIONS: The risk factors identified in our study should prove useful for designing preventive strategies, thereby improving the quality of care.