Doppler evaluation in erectile dysfunction (ED) has a significant role in determining the cause of ED. The advantages of penile Doppler and pharmacologic duplex ultrasonography include objective, minimally invasive evaluation of penile hemodynamics at a relatively low cost. Arteriogenic ED may be secondary to peripheral vascular disease and diabetes, or may be seen in association with coronary artery disease. Various parameters, such as diameter of the cavernosal artery, peak systolic flow velocity, degree of arterial dilatation and acceleration time, have been suggested for the diagnosis of arteriogenic ED, but peak systolic flow velocity is the most accurate indicator of arterial disease. This second part of the review article describes the various causes of ED and the interpretation and evaluation of color flow Doppler examination in ED.