Aim: Thromboembolism is common in patients with cancer and may be considered a major cause of morbidity and mortality. We studied the most common genetic polymorphism characteristics that may have roles in the development of thrombosis in patients with cancer. Methods: A total of 158 patients with cancer who had had any thrombotic event were included, together with a control group of 134 patients with cancer without a thromboembolic event. The presence of mutations (Factor V Leiden G1691A, prothrombin G20210A) and polymorphisms (methylenetetrahydrofolate reductase [MTHFR] C677T and plasminogen activator inhibitor (PAI-1) 4G/5G) were analysed. Results: A heterozygous polymorphism for Factor V Leiden G1691A was found in 48 patients (30.3%) and a homozygous polymorphism in only one (0.63%), compared to 32 heterozygous (23.8%) and one homozygous (0.74%) polymorphism in the control group (P = 0.462). Prothrombin G20210A heterozygous polymorphism was observed in 11(6.9%) and four (2.5%) in the patients and controls, respectively. The MTHFR C677T heterozygous polymorphism was found in 48 (30.3%) and 24 (15.1%) and the homozygous polymorphism was observed in 15 (9.4%) and 12 (7.5%) in the study and control group, respectively (P = 0.04). Conclusion: Although we found a statistically significant difference between patients with and without thrombosis in respect to MTHFR C677T gene mutation, our data suggest that we do not have enough evidence yet to recommend performing genetic analysis.