Two cases are reported of intravenous leiomyomatosis with extension of neoplastic thrombus to the right atrium; an histological documentation of each patient has been successfully obtained during surgical procedure. International literature is reviewed and a useful diagnostic protocol for the correct evaluation of these patients is suggested, in order to choose the best surgical approach. The important role of CT with intravenous injection of contrast medium is pointed out. The advantages resulting from the use of echotomography and from angiographic study of the inferior vena cava are stressed.