The case of a 48-year-old woman in whom focal nodular hyperplasia of the liver developed after busulfan therapy was administered for essential thrombocytosis is described. Focal nodular hyperplasia is a reactive disorder related to a circulation disorder. The close temporal relation between the haematological disease, busulfan treatment and the appearance of hyperplastic diseases of the liver in our patient supports the possibility that the association of the events might not be casual.