cytokeratin-19 fragment (CYFRA21-1) is a soluble protein in serum, and may be a useful circulating tumor marker. The aim of this study is to investigate the diagnostic value of the peripheral blood CYFRA21-1 in non-small cell lung cancer (NSCLC).the levels of peripheral blood CYFRA21-1 were detected in 107 patients with NSCLC and 51 patients with benign pulmonary diseases by enzyme linked immunosorbent assay, and ROC curve was used to analyse the results.singificant difference of peripheral blood CYFRA21-1 levels was detected between the NSCLC group and benign pulmonary disease group (Chi-Square=47.343, P < 0.001). At the threshold of 3.3 ng/mL, sensitivity and specificity of CYFRA21-1 as a serologic marker were 74.77% and 76.47%, respectively for any cancer. ROC curve showed that the under-curve area (AUC) of CYFRA21-1 was 0.813 9. There was no significant difference of CYFRA21-1 between subtypes of NSCLC (Chi-Square=0.450, P=0.799). The peripheral blood CYFRA21-1 level was elevated significantly in the patients with extensive disease (IIIb, IV) compared with patients with limited disase (I, II, IIIb) (Chi-Square=7.057, P=0.008).as a tumor marker CYFRA21-1 has relative high sensitivity and specificity for the diagnosis of NSCLC. Elevated peripheral blood CYFRA 21-1 levels were usually indicated extensive disease of NSCLC.