Forty-eight cyclists were studied for suspected external iliac artery endofibrosis with ultrasound B-mode imaging. In highly trained competition cyclists, symptoms of external iliac artery endofibrosis were characterized by lower limb claudication during maximal effort that was caused by fibrosis thickening of the intima of the external iliac arterial wall. Typical ultrasound imaging aspects consisted of parietal thickening, enhanced echogenicity of the arterial wall, straightness of the abnormal arterial segment, and mild narrowing of the arterial diameter of the proximal or medial segment of the diseased external iliac artery. Although ultrasound B-mode imaging study seems to be useful in the diagnosis of external iliac artery endofibrosis, results with this technique must be compared with results of clinical examination, physiologic tests, and arteriography.