In a 4-year prospective quality assurance study, 315 iatrogenic medication errors were reported among the 2147 neonatal and paediatric intensive-care admissions, an error rate of 1 per 6.8 admissions (14.7%). The frequency of iatrogenic injury of any sort due to a medication error was 66/2147 (3.1%)--1 injury for each 33 intensive-care admissions. 33 (10.5%) errors were potentially serious, 32 (10.2%) caused mild patient injuries, and 1 patient had acute aminophylline poisoning after receiving five intravenous doses of the drug at a dosage ten times higher than prescribed, owing to a calculation error during dilution. A longitudinal monitoring system helps to identify iatrogenic complications due to medication errors and may help in implementing preventive measures.