A significant number of children receive either an unlicensed or an off-label drug during their stay in hospital. Studies throughout Europe have shown that at least one-third of children in hospital and up to 90% of neonates in a neonatal intensive care unit receive such drug prescriptions. The medicines that are most frequently used off-label include analgesics, antibiotics and bronchodilators. The purpose of licensing a drug is to ensure safety, efficacy and quality. If a drug is used in a different manner, one would expect a greater risk of toxicity. Only three studies have commented on the risk of toxicity in relation to unlicensed or off-label drug use. Only one of these three studies prospectively tried to evaluate the risk associated with off-label and unlicensed drug prescription. This study suggested that the percentage of unlicensed and off-label drug use was significantly associated with the risk of an adverse drug reaction. Two studies looking at adverse drug reactions suggest that there is a greater risk of a severe adverse drug reaction occurring in association with the off-label or unlicensed use of drugs. One study found that five out of eight severe adverse drug reactions were associated with the off-label use of a medicine. The other study found that 14 of 19 drug prescriptions associated with 17 severe adverse drug reactions were either unlicensed or off-label. The risk of prescribing off-label and unlicensed drugs in children is not clear from the limited data available.