Emerging data have enhanced our understanding of cancer-associated thrombosis, a major cause of morbidity and mortality in patients with cancer. This update will focus on recent findings, including the phenomenon of incidental venous thromboembolism (VTE), novel approaches to risk assessment, and the results of randomized clinical trials focusing on prophylaxis of cancer outpatients. Incidental VTE is an important contributor to rates of cancer-associated VTE and, in terms of outcomes, appears to be as consequential for patients as symptomatic VTE. Multiple biomarkers have been studied, with the highest level of evidence for prechemotherapy elevated platelet counts, elevated leukocyte counts, and low hemoglobin. Other candidate biomarkers, including D-dimer and tissue factor, are currently being evaluated. A recently validated risk score for chemotherapy-associated VTE has now been evaluated in more than 10 000 cancer patients in a variety of clinical settings and trials and is ready for clinical use (Level 1 clinical decision rule). Several randomized clinical trials in solid-tumor patients with low-molecular-weight heparins and semuloparin, an ultra-low-molecular-weight heparin, demonstrate clearly that outpatient thromboprophylaxis is feasible, safe, and effective. Selecting the appropriate patients for prophylaxis, however, continues to be a matter of controversy.