BACKGROU ND: This study evaluated the accuracy of duplex ultrasonography (DUS )-based peak systolic velocity ratio (PSVR) and ipsilateral common femoral artery (CFA) velocity waveform analysis to identify a hemodynamically significant equivocal iliac artery stenosis (30-75% lumen diameter reduction). Intra-arterial pressure measurements were used as a reference. METHODS : In a previously performed prospective study (NTR5085), 30 patients with 35 iliac artery stenoses underwent intra-arterial angiography. To determine the hemodynamic significance of the iliac artery stenoses, intra-arterial translesional pressure measurements were performed under hyperemic conditions. Preprocedural DUS was obtained of the iliac and femoral arteries. PSVR over the iliac lesions was determined, and ipsilateral CFA velocity waveforms were retrospectively classified. The intraobserver and interobserver agreement for CFA velocity waveform classification were evaluated. Sensitivity, specificity, and overall accuracy were calculated by comparing PSVR, velocity waveform analysis, and a combination of these parameters to the intra-arterial translesional pressure gradient. A translesional pressure gradient ≥10 mmHg, PSVR ≥2.5, and a monophasic or biphasic CFA velocity waveform were considered to be indicative for a hemodynamically significant iliac artery stenosis. RESULTS: For classification of ipsilateral CFA velocity waveforms, intraobserver and interobserver agreement were 0.94 and 0.82, respectively. A PSVR ≥2.5 could identify a hemodynamically significant stenosis with 83% sensitivity, 67% specificity, and an overall accuracy of 77%. When both a monophasic and a biphasic velocity waveform were considered to indicate a hemodynamically significant iliac artery stenosis, sensitivity was 78%, specificity was 50%, and the overall accuracy was 69%. The combination of a PSVR ≥2.5 with either a monophasic or a biphasic CFA velocity waveform was found in 20 stenoses and resulted in 94% sensitivity, 75% specificity, and 90% accuracy. When the remainder of the stenoses (N.=15) was classified by means of the PSVR, the overall accuracy remained 77%. CONCLUSIONS: DUS is a very useful noninvasive imaging modality to determine the significance of an iliac artery stenosis. A combination of translesional PSVR ≥2.5 with either a monophasic or a biphasic ipsilateral CFA ultrasound waveforms has a good accuracy and helps to select patients that benefit most from follow-up examination by computed tomography angiography or magnetic resonance angiography.