This review discusses case reports of patients treated with psychotropic medications for which therapeutic drug monitoring (TDM) was found useful. The use of this approach is based on the assumption that previous papers on TDM have largely used the available database of controlled studies to establish that excessively low concentrations of antidepressants, antipsychotics or mood stabilisers often lead to poor treatment response, whereas excessively high concentrations are associated with an increased risk of unwanted side effects and even poor response for some drugs.Typical situations in which TDM has been found to be clinically useful include poor compliance, patients who are ultra-rapid or poor metabolisers, elderly patients, instances of metabolic inhibition and induction, and patients with liver dysfunction.In order to provide clinically relevant information, certain practical aspects of TDM must be respected. The results of the assays must be rapidly available to the treating physician, selection of medications to be monitored must be based on the daily practice in the given psychiatric institution, analytical methods must be specific, and numerical results should be complemented by a short written comment.Under these conditions, TDM in psychiatry is a cost-effective means to assessing compliance, enhancing therapeutic response, avoiding toxicity, increasing quality of life and improving the therapeutic alliance.