Errors in prescription, administration, delivery and interaction of drugs are likely in children in intensive care units because of the large number of often unfamiliar medications these children receive. We evaluated prospectively the frequency and consequence of drug errors in a large multidisciplinary intensive care unit. There was a mistake in drug prescription, administration, delivery or drug interaction in 2% of medication orders, with 12% of these mistakes causing actual harm to the patient. The frequency of drug errors must be appreciated and due care must be taken in checking and delivering drugs to children in an intensive care unit.