The therapy of children and adolescents with psychotropic drugs differs from that of adults. Due to the differences in the pharmacokinetic behaviour of the drugs used that are dependent on a child's, respectively an adolescent's stage of development, the same dosages as recommended for adults cannot be used. Moreover, many of the drugs used have not been approved for use in children and adolescents. Thus the criteria which guarantee their efficacy and safety for use in adults do not apply for their use in children and adolescents. Therefore therapeutic drug monitoring (TDM) is a general indication for the administration of psychotropic drugs in children and adolescents. TDM enables the clinician to adjust the dosage of a drug according to the characteristics of the individual patient. It is also a valid tool to increase the safety of therapy and optimise therapy with psychotropic drugs. However, standardized studies are also needed to find therapeutic ranges of plasma concentrations for children and adolescents. Such studies will deliver new insights into the pharmacokinetic and pharmacodynamic behaviour of drugs used in child and adolescent psychiatry. The present contribution begins with a brief description of the strategy of TDM in psychiatry, followed by a discussion of the characteristics of pharmacotherapy in child and adolescent psychiatry and the reasons for the general indication of TDM in children and adolescents. Finally, recommendations are given for the routine performance of TDM. For a detailed treatment of TDM in psychiatry, the interested reader is referred to the AG-NP-TDM Expert Group Consensus Guidelines published earlier (Baumann et al., 2004).