Osteonecrosis is a rare complication of HIV infection. The presumptive cause of the aseptic osteonecrosis is a disturbed blood supply to the bone. Most cases of osteonecrosis are associated with numerous risk factors, such as use of steroids, alcohol abuse, coagulopathies or metabolic derangements. Since conventional X-rays appear unremarkable, early forms often go unrecognized or are diagnosed late. Methods of establishing the diagnosis are NMR and three-phase skeletal scintigraphy. The pathogenesis of osteonecrosis in HIV infection is unclear. So far, about 30 cases have been reported in the literature. Since a number of these cases had no classical risk factors, it is assumed that the HIV infection itself is the causative agent. In other patients anticardiolipin antibodies, which are considered to be a risk factor, are found. Other HIV patients with aseptic osteonecrosis have elevated blood lipids; changes in blood fats have long been established as a risk factor in osteonecrosis. Furthermore, an association of osteonecrosis with proteinase inhibitor-induced metabolic lipid disorders was reported. Whether the risk for osteonecrosis in treatment with proteinase inhibitors actually is raised, or whether the association is a coincidence needs further investigation. We would recommend that in HIV patients with typical symptoms--in particular when classical risk factors are present--osteonecrosis be included in the differential diagnostic considerations.