Cystatin, a proteinase inhibitor, is involved in the intracellular catabolism of proteins. We investigated the change in concentration of serum Cystatin C (CysC) in children with lymphomas and its diagnostic utility. Twenty-eight newly diagnosed patients with lymphoma were included in this study. The male/female ratio was 20/8, with a median age of 8.5 years (range 3-17 years). Thirteen patients had Hodgkin's lymphoma (HL) and 15 had non-Hodgkin's lymphoma (NHL). Cystatin C concentration was determined at the time of diagnosis and during remission.