The anatomy of intra‐osseous vessels of bones distal to a femoral or an iliac arteriovenous fistula was studied by histologic and microangiographic methods. The venous and sinusoidal vessels were dilated and heavily filled with contrast medium from 3 to 60 weeks after construction of the fistula. The nutrient artery and its branches are smaller in caliber in bones distal to the fistula at three weeks but appeared to return to approximately normal size later in the experimental period. The anatomic findings appear to provide an important link in a hypothesis to explain the increase in total bone seen distal to an arteriovenous fistula. Copyright © 1968 Wiley‐Liss, Inc.