A variety of factors have been proposed to explain arteriovenous fistula primary failures in patients undergoing hemodialysis, including obesity, diabetes mellitus, female sex, and the absence of preoperative vein mapping. In this report, we describe 2 women for whom premature upper-extremity arteriovenous fistula failures occurred in the setting of venographic evidence of soft-tissue compression of the venous outflow with the patient's arm in the adducted position. In each instance, preoperative noninvasive duplex vein mapping showed veins of adequate diameter (0.28 to 0.54 cm), and further evaluation showed no evidence of a hypercoagulable state. Upper-extremity venography was used to assess central venous patency and fully assess the venous vasculature. Unlike the widely patent venous systems seen in the abducted position, venography performed with the upper extremities in adduction showed marked narrowing of the brachial and/or axillary veins. The hemodynamic effects of this narrowing were readily apparent in patient 2 with the appearance of collateral filling of the cephalic vein in the adducted position. Patient 1 had a body mass index of 39 kg/m(2), and patient 2 had a body mass index of 34 kg/m(2). Each patient had excess axillary soft tissue that appeared to compress the venous outflow in adduction. To our knowledge, this is the first report to radiographically document soft-tissue compression of the venous outflow of the upper extremity in the adducted position, suggesting a mechanism whereby obesity, or at least excess axillary fat, can lead to premature hemodialysis vascular access failures.