Throughout the world, many drugs prescribed for children are used in an off-label or unlicensed manner. The incidence of unlicensed and off-label drug prescriptions appears to be greatest in critically ill neonates and children and lowest in the general population. The risk associated with unlicensed and off-label drug use appears to be greater than for prescribing in accordance with the product licence. Health professionals, however, usually have no alternative but to use unlicensed and off-label medicines. More clinical trials for medicines in children are required to provide the evidence base for safe and effective drug prescribing.