To study the revascularization pattern of nontraumatic osteonecrosis, superselective angiography of the femoral medical circumflex artery was done twice on 13 hips for which no treatment had been given. Angiographic evaluation of the hips with early-stage osteonecrosis not visible on radiographs showed the absence of superior retinacular arteries from the stump in all hips. Penetration of small vessels was seen on 6 hips. Bony scintigraphy of 13 hips and magnetic resonance imaging of 9 hips were taken at about the same time. Bony scintigraphy and magnetic resonance imaging results were positive in 11 of 13 hips and in all 9 hips, respectively. The patients were observed until evidence of necrosis appeared on radiographs. When this sign became evident, a second angiography was conducted, which indicated the penetration of erratically formed vessels with increase in size in 12 hips. It was assumed that the blood supply from the superior retinacular arteries was interfered with in large areas of the femoral head and that revascularization started with the formation of small vessels, followed by further penetration of large vessels.