The introduction of tyrosinekinase inhibitors has revolutionized treatment of patients with solid and hematologic malignancies. Treatment with these drugs is often performed according to the ‘one-dose-fits-all’ paradigm at the outpatient clinic. This is practical for both patients and physicians, but most likely not the best way of treating patients. Several factors may influence the systemic exposure to these drugs with sub-therapeutic or toxic concentrations as a result. A common method to individualize dosing is by means of ‘therapeutic drug monitoring’ (TDM). TDM aims to individualize dosing based on plasma concentrations. In this article we discuss the state of affairs of this technique to individualize tyrosine kinase inhibitor dosing and we give a practical guideline to perform TDM. Although often prospective evidence is lacking, TDM has the potential to further improve precision medicine.