Background and aims: In lung cancer, many factors have prognostic significance, including thrombocytosis, which is frequently observed. Associations between vascular events, which are the outcomes of paraneoplastic symptoms, and mortality and morbidity has been evaluated in many studies. The aim of the present study was to evaluate the relationship between thrombocytosis and vascular events. Materials and Methods: In total, 281 patients, who were histopathologically diagnosed with lung cancer between March 2007 and August 2009, were evaluated retrospectively. Data analysis was performed using the Statistical Package for the Social Sciences (SPSS) software (ver. 11.5 for Windows). Analysis of the distribution of constant variance for normality was assessed using the Shapiro-Wilk test. Nominal variables were evaluated using Pearson's chi-squared or Fisher's exact chi-squared tests. Significant correlations between continuous variables were investigated using Spearman's correlation test. Results: Of the 281 patients, 234 (83.3%) were males and 47 (16.7%) were females, with a median age of 60.6 (31-83 years). Histopathologically, 40 (14.2%) were diagnosed with small-cell lung cancer and 241 (85.8%) with non-small cell lung cancer. In total, 17 (6.04%) vascular events were identified: 11 (64.7%) deep vein thromboses, three (17.6%) pulmonary thromboembolisms, one (5.9%) cerebral arterial thrombosis, and one (5.9%) vena cava superior thrombosis. Thrombocytosis was not determined during thrombosis, but during subsequent visits. Conclusions: Thrombocytosis is frequently observed in patients with lung cancer. Further prospective studies are required to evaluate the need for prophylactic anticoagulants in these patients. The association between vascular events and survival, the next step of the present study, will be evaluated prospectively.