Both in the development of medicinal products as well as in risk assessment of other xenobiotics there is an increasing awareness that children should be considered as a special group. Children are exposed to other doses than adults and the pharmacokinetics and pharmacodynamics can be very different in children and adults. In general it can be concluded that the effects of age on pharmacokinetics are most pronounced during the first 6-12 months of life. Full adjustment of dosing or TDI's for pharmacokinetic differences can relatively easily be applied and should, to our opinion be seen as a first step in considering risk for the paediatric population. For risk assessment for drugs as well as for other xenobiotics, it seems to be essential that young animal models will be used for determining NOAELs, that are relevant for the paediatric population. The use of a paediatric PBPK model possibly combined with pharmacodynamics (PBPK/PD model) may be a valuable aid in risk assessment.