Laboratory investigation of thrombophilia is aimed at detecting the well-established hereditary and acquired causes of venous thromboembolism, including activated protein C resistance/factor V Leiden mutation, prothrombin G20210A mutation, deficiencies of the physio - logical anticoagulants antithrombin, protein C and protein S, the presence of antiphospholipid antibodies and increased plasma levels of homocysteine and coagulation factor VIII. In contrast, investigation of dysfibrinogenemia, a very rare thrombophilic risk factor, should only be considered in a patient with evidence of familial or recurrent thrombosis in the absence of all evaluated risk factors mentioned above. At this time, thrombophilia investigation is not recommended for other potential hereditary or acquired risk factors whose association with increased risk for thrombosis has not been proven sufficiently to date. In order to ensure clinical relevance of testing and to avoid any misinterpretation of results, laboratory investigation of thrombophilia should always be performed in accordance with the recommended guidelines on testing regarding the careful selection of patients, time of testing and assays and assay methods used. The aim of this review is to summarize the most important aspects on thrombophilia testing, including whom and when to test, what assays and assay methods to use and all other variables that should be considered when performing laboratory investigation of thrombophilia.