Coumarinic oral-anticoagulants (COAs) are commonly used for treatment of thromboembolic events. However, these medications have a narrow therapeutic range and there are large inter-individual variations in drug response. This is especially important in the initial phases of oral-anticoagulant therapy. Recent advancements in pharmacogenetics have established that clinical outcomes in oral-anticoagulant therapy are affected by genetic factors. The allelic variants of genes like cytochrome P450 2C9 (CYP2C9) and vitamin K epoxide reductase complex subunit 1 (VKORC1) are closely associated with maintenance dose of oral anti-coagulants. In addition, GGCX (Gamma-glutamyl carboxylase) polymorphism at position 12970 (rs11676382), CYP4F2 (rs2108622; V433M; 1347 C > T) and Apolipoprotein E (APOE) variants have been shown to explain a small but significant influence on dose requirements. There are large differences in the frequencies of these polymorphisms between different world populations which are also related to the requirements of oral anticoagulants. However, the final drug dosage in an individual is determined by complex sets of genetic and environmental factors and several dosing algorithms which combine clinical and genetic parameters to predict therapeutic COA doses have also been developed. The algorithm based dose prediction shows the importance of pharmacogenetic testing in patients undergoing oral anticoagulant therapies.