Background: Chemotherapy induced leutropenia has been shown to be associated with improved treatment outcomes in selected solid tumors. We studied the association of chemotherapy induced leutropenia with treatment related outcomes in advanced non-small-cell lung cancer. Methods: This is a prospective analysis of patients receiving chemotherapy for advanced NSCLC at the Shandong Cancer Hospital from 2005-07.The chemotherapy included cisplatin $35mg/m^2$, IV on $d_{1,2}$ and vinorelbine $25mg/m^2$ IV on $d_{1,8}$ every 21 days. Patients were stratified into three groups (A) those experiencing grades 0 leucopenia, group (B) grades 1-2 and group (C) grades 3-4. The outcomes studied were response rate (RR), disease control rate (DCR), and time to progression (TTP). Results: 128 patients were studied. The RRs in groups A, B and C were 30.8%, 56.8% and 71.4%, respectively, p=0.010. The DCRs were 61.5%, 83.8% and 92.9%, respectively, p=0.009 and the median TTPs were 150 days (95%CI: 91-209), 189 days (95%CI: 181-197) and 207 days (95%CI: 172-242), p=0.009. The differences in RR and TTP were significant. In patients whose CIL kept on 10 days at least, the TTP was significantly prolonged, p=0.0213, and the same was the case for those experiencing grades 1-2 leucopenia and ECOG 0, p=0.0412. Conclusions: Occurrence of CIL correlated with RR and TTP in patients with advanced NSCLC receiving cisplatin and vinorelbine chemotherapy, especially in patients experiencing grades 1-2 leucopenia and ECOG 0, and the same for those with CIL persisting for 10 days at least. CIL could be a biological measure of drug activity and a marker of efficacy.