Many hospitalized patients are under an increased risk of venous thromboembolism. They should have adequate pharmacological prophylaxis. Clinical studies including meta-analyses prove that low molecular weight heparin prophylaxis of venous thromboembolisms is equally effective as that employing unfractionated heparin and it features less bleeding complications. The effectiveness of pharmacological prophylaxis with low molecular weight heparin in hospitalized patients at internal medicine departments has been proven by the MEDENOX study when enoxaparin in a dose of 40 mg was administered subcutaneously and the PREVENT study when subcutaneous dalteparin 5 000 units j. was administered daily. In the MEDENOX study, enoxaparin administration was confirmed to decrease the relative risk of venous thromboembolisms by 63% without increasing any adverse effects during the prophylaxis and the PREVENT study showed that dalteparin administration was followed by a highly significant reduction of asymptomatic venous thromboses in hospitalized patients. According the ACCP guideline for thromboprophylaxis in hospitalized internal medicine patients with clinical risk factor of venous thromboembolism (tumors, heart failures, sepsis, VTE history and serious pulmonary condition), low molecular weight heparin or mini-doses of unfractionated heparin are to be administered. The recent recommendations discourage the use of acetyl-salicylic acid in monotherapy treatment for venous thromboembolism prevention.