Quantification of luminal dimensions and the mechanisms by which angioplasty (PTA) corrects non-atheroma venous fistula stenoses have been poorly studied. In 38 consecutive percutaneous balloon angioplasties of hemodialysis fistula stenoses, catheter-based, mechanically-rotated intravascular ultrasound (IVUS) images were obtained along with cineangiography. Images from 24 brachial vein, 11 central vein, 2 graft anastomoses, and 1 brachial artery were quantitatively and qualitatively evaluated. Semiautomated quantitative angiographic stenosis was 64 +/- 13% pre-PTA and reduced to 36 +/- 19% post-PTA (P less than 0.001). Post-PTA IVUS minimal lesion diameter and cross sectional area were 5.7 +/- 1.5 mm and 2.9 +/- 1.5 mm2, respectively. With IVUS, mechanisms observed were: vessel dissection in 16 (42%), arterial stretch (defined as vessel diameter: balloon diameter ratio = 0.75 to 1.0) in 19 (50%), and elastic recoil (defined as vessel diameter: balloon diameter ratio less than 0.75) in 19 (50%). Compared to angiography, morphologic information provided by IVUS were plaque composition (hard 11%, soft 89%), plaque topography (eccentric 94%, concentric 6%), thrombus (IVUS: N = 6 vs. angio: N = 1), dissection (IVUS: N = 16 vs. angio: N = 1). Thus, IVUS can evaluate lesion morphology and define luminal dimensions after angioplasty. Mechanisms of successful angioplasty of hemodialysis fistula stenosis occur primarily by vessel stretching and dissection, and significant post-PTA narrowing is due to elastic recoil.