The purpose of this study was to determine the feasibility of helical CT phlebography of the superior vena cava (SVC) and to evaluate the role of this imaging technique in the diagnosis and treatment of SVC obstruction. Twenty-three helical CT phlebograms were obtained of patients with clinical findings that were suggestive of SVC obstruction (n = 19) and of patients undergoing posttherapeutic evaluation for SVC obstruction (n = 4). CT examinations consisted of helical acquisitions obtained in the craniocaudal direction with simultaneous bilateral antecubital vein injection of 2 x 90 ml of 12% iodinated contrast material at 2 ml/sec. Combined analysis of axial, multiplanar, and maximum-intensity-projection reformatted images was used for all patients. Image quality, venous stenosis or obstruction, intraluminal thrombus, and collateral pathways were evaluated. Comparison with digital phlebographic data was available for 16 patients; this comparison was performed in a nonblinded manner. CT phlebograms were considered technically optimal in 91% of the patients. In all these patients, helical CT phlebograms showed the venous obstruction: the site, extent, cause, and collateral pathways. CT phlebography appeared to be well correlated with digital phlebography in 16 patients regarding the degree of obstruction, the presence of collateral pathways, and the presence of thrombus. Helical CT phlebography may be a useful technique for imaging the SVC and its tributaries. This imaging technique is simple to perform and can provide all the information necessary to diagnose and treat SVC obstruction.