Venous thrombosis involving the deep veins is a major US health problem that affects over 2.5 million people annually. The most serious complication of a deep venous thrombosis (DVT) is pulmonary embolism (PE), which is associated with 50,000 to 200,000 deaths each year. DVT and PE are often silent and difficult to detect by clinical examination; however, DVT rarely occurs in the absence of risk factors. This article reviews normal venous anatomy and discusses the etiology of DVT, its clinical manifestations, and diagnosis. Then it reviews treatment of DVT, highlighting the nurse's role. A discussion of DVT prophylaxis based on patient risk follows.