Coumarin is an effective treatment for primary lymphoedema, as well as lymphoedema related to breast cancer radiotherapy or surgery. However, its clinical use is limited in several countries due to the possible occurrence of hepatotoxicity, mainly in the form of mild to moderate transaminase elevation. Noteworthy, only few cases of severe hepatotoxicity have been described in literature, with no reported cases of liver failure. Data available on coumarin absorption, distribution, metabolism and excretion have been reviewed, focusing on hepatotoxicity studies carried out in vitro and in vivo. Finally, safety and tolerability data from clinical trials have been thoroughly discussed. On the basis of these data, coumarin-induced hepatotoxicity seems to be restricted to a small subset of patients, probably due to the expression of specific alleles of CYP450 isoform not yet well characterized. In summary, more research is needed in order to identify patients at risk of developing hepatotoxicity following coumarin treatment, in order to improve the risk/benefit ratio of the product and allow more patients to benefit from its therapeutic properties.