Insufficiency fractures often occur in the sacrum and pubic rami but have rarely been reported in the ilium, where their frequency may be underestimated. We studied a series of 14 patients with insufficiency fractures of the ilium. Six patients had an oblique fracture through the wing of the ilium (which was bilateral in one case) and nine a supraacetabular fracture, with in one case a superomedial extension into the iliac wing. The initial radiographs were normal, making the diagnosis difficult. A linear area of sclerosis along the fracture line was seen after a few weeks. The radionuclide examination provided early detection and often demonstrated multiple insufficiency fractures (mean 2.1 per patient). Computed tomography missed some of the fractures, whereas magnetic resonance imaging proved a reliable diagnostic tool, especially in patients with supraacetabular fractures, showing the fracture as a line of low signal surrounded by an area of edema whose contours were exactly the same as those of the hyperactive focus on the radionuclide scan. Osteoporosis was a causative factor in all 14 patients and vitamin D deficiency in seven. Also, three patients had a history of fluoride therapy.