Approximately 20-25% of all new cases of venous thromboembolism occur in known cancer patients. The risk of VTE is 4-6 fold greater in patients with cancer as those without (8-12% vs. 2%, respectively, lifetime risk). In many cases, the development of VTE occurs as the first clinical sign of the cancer, even before it is diagnosed. Among patients presenting with acute VTE have no obvious cause (defined as "idiopathic" or "unprovoked", as opposed to "secondary" VTE), the literature reports that up to 20% (range of reported incidence 7-20%) may ultimately prove to have cancer, depending on the series and whether the thrombosis is unifocal or multifocal. Despite the substantial prevalence of occult cancer in patients presenting with idiopathic VTE, there are no current recommendations that these patients be screened for the presence of cancer. The second hypothesis of the project is that FDG PET/CT can accurately be used to screen for the presence of cancer in patients with unprovoked (idiopathic) acute VTE.