e18531 Background: Activated platelet is thought to promote cancer cells growth and metastasis, playing an important role in progression of cancer. However, the association between platelet counts and prognosis of patient with non small cell lung cancer (NSCLC) had not been fully elucidated. The aim of this study is to investigate the prognostic value of platelet counts in resectable NSCLC. Methods: A total of 636 primary NSCLC patients who had curatively resected surgery in Zhejiang Cancer Hospital from November 2006 to January 2011 were retrospectively analyzed. Preoperative platelet counts and clinicopathological factors were collected from the medical record database. Patients were followed up for disease progression free survival (PDS) and overall survival (OS) until January 20, 2013. The association between platelet counts and patients’ outcome were evaluated. Results: In all patients, 13.8% (88/636) had increased platelet count (>300 × 109/L), referred to as thrombocytosis. The proportion of thrombocytosis was significantly higher in male, squamous-cell carcinoma and stage III than that in female, other histological types and early stage NSCLC. Moreover, thrombocytosis was associated with significantly shortened survival. Multivariate Cox analysis showed patient with thrombocytosis not only had a 1.66 time elevated risk for disease progression (95% CI, 1.14-2.41, p=0.009), but also had and a 1.47 time risk for death (95% CI, 1.04-2.08, P=0.029), compared with that in those having normal platelet count. More interestingly, the risk for replase was increased to 3.19 times (95% CI, 1.41-7.23, p=0.006) in stage I NSCLC with thrombocytosis than that in patients with normal platelet count after stratified analysis by stage. Conclusions: Preoperative platelet count is an independent prognostic predictor in operable NSCLC, especially in early stage I NSCLC. Platelet count may serve as a useful indicator and potential target for personalized treatment with antiplatelet reagent.