Patients with clinical conditions such as surgery, trauma, and acute medical illness have a transiently increased risk of venous thromboembolism and merit consideration for adequate thromboprophylaxis. The choice of an appropriate pharmacologic or physical means of prophylaxis should be made taking into account both the thrombotic and bleeding risk associated with patient-related factors and the type of surgery or other disease state involved. A large number of randomized clinical trials, meta-analyses, and guidelines developed by scientific societies worldwide have addressed this issue and have provided information and recommendations that should be considered carefully. The aim of this review is to provide the practicing physician with a brief updated summary of the subject, stratifying those patients at low thrombotic risk who do not require specific thromboprophylaxis apart from early ambulation, from those at moderate or higher thrombotic risk