L-asparaginase and glucocorticosteroides are the main drugs used in the first-line treatment in children with acute lymphoblastic leukaemia. One of the observed side effects in the increase of serum level of triglycerides is synergistic manner. The paper describes two children with acute lymphoblastic leukaemia. In these patients we could observe remarkable hypertriglyceridemia, and hypercholesterolaemia with the increase of LDL-cholesterol after applying high doses of L-asparaginase and glucocorticosteroids simultaneously. The above-mentioned disorders were transient. In the analysis of the possible reasons of this pathology we took into consideration family predispositions, the transient deficit of lipoprotein lipase induced by L-asparaginase, improper diet and hyperthyroidismus.