The present study investigates the validity and accuracy of the modified Bernoulli equation in the Doppler-derived evaluation of pressure drops across peripheral artery stenoses. Conventional duplex-derived (x) and catheter-measured (y) mean and peak pressure gradients across iliac artery stenoses were determined in 35 iliac arteries of 28 patients. The correlations between both methods were r = 0.84 (n = 35; SEE = 4; y = 0.89x + 2) for the mean and r = 0.86 (n = 27; SEE = 10; y = 0.76x + 11) for the peak pressure gradients. In a second study, color-coded duplex-derived (x) and catheter-measured (y) pressure gradients across iliac artery stenoses were determined in 28 further patients. The correlations were 0.86 (n = 28; SEE = 5; y = 0.98x + 0.5) for the mean and r = 0.83 (n = 18; SEE = 15; y = 0.83x + 4) for the peak pressure gradients. These data show that the modified Bernoulli equation can be applied to predict pressure gradients across iliac artery stenoses in patients with peripheral artery diseases.