Venous thromboembolism (VTE) consists of two related conditions: pulmonary embolism (PE) and deep vein thrombosis (DVT). Objective testing for VTE is crucial because the clinical diagnosis is nonspecific and insensitive, and the consequences of a missed diagnosis are serious. The purpose of this review is to discuss the utility of venous ultrasonography as the foundation for diagnosis of acute lower extremity DVT. The effectiveness and practicality of venous ultrasonography as a stand-alone examination versus theoretically attractive, but perhaps less practical, combined approaches of ultrasonography with clinical probability assessment and D-dimer testing in the diagnosis of acute DVT is also addressed. Finally, the role of venous ultrasonography in a diagnostic algorithm for suspected PE is discussed.