1. A vein, designated the vein of the lateral recess of the fourth ventricle (VLR), is described which has unique anatomic relationships to the fourth ventricle and adjacent adjacent structures. Recognition of this vessel on angiography makes it possible to localize these structures.2. Tributaries of the VLR can often be identified if filling is satisfactory. These include parenchymal, subependymal, medial and lateral tonsillar, and supratonsillar veins.3. The roentgen appearances of the VLR and its tributaries are illustrated in injected specimens and in vivo. The anatomic relationships are described in detail and correlated with air studies.4. The diagnostic value of the VLR is briefly demonstrated by illustrations of an arteriovenous malformation and tumors of the fourth ventricle.