In psychiatry, therapeutic drug monitoring (TDM) is an established procedure for most psychotropic drugs. However, as its use in everyday clinical practice is far from optimal, the AGNP-TDM group has worked out consensus guidelines to assist psychiatrists and laboratories involved in drug analysis. Based on a thorough analysis of available literature, 5 levels of recommendation were defined with regard to TDM of psychoactive drugs, from 1) (strongly recommended) to 5) (not recommended). A list of indications for TDM, alone or in combination with pharmacogenetic tests is presented. Instructions are given with regard to preparation of TDM, analytical procedures, reporting and interpretation of results and the use of information for patient treatment. Using the consensus guideline will help to ensure optimal clinical benefit of TDM.