The interindividual variability in pharmacokinetics represents one of the factors involved in difference of both efficacy and toxicity of anticancer drugs prescribed to patients with the same cancer disease. The causes of pharmacokinetic interindividual variability are themselves divers. The impaired organic function corresponding either to liver or kidneys represents the major cause since any impaired function is systematically responsible of pharmacokinetic modifications, and due to the amplitude of these modifications. In this article, the clinically relevant pharmacokinetic parameters are shown. The methodologies used to study the pharmacokinetic variability due to impaired organic functions and to control them are detailed.