Although treatment of children infected with HIV with protease inhibitors has improved the survival of these patients, various adverse side effects have been reported, including metabolic abnormalities, such as hyperlipidaemia. We describe a case of hip osteonecrosis in an adolescent with AIDS who was being treated with protease inhibitors. There is a possible relation with hyperlipidemia. F.M.G., white, 11 years old, AIDS A2, started to receive AZT and DDI when he was 7 years old. In April 1999, the patient had a significant increase in viral load and so the antiretroviral therapy was switched to d4T, 3TC and Ritonavir. Triglyceride plasma levels reached 460mg/dl after this switch and were always above the reference value. In December 1999, the patient complained of pain in the right hip. On physical examination, he had limited movement of this joint. Magnetic resonance imaging of the right hip showed flattening, deformity and fragmentation of the femoral head, compatible with osteonecrosis. Few cases of femoral head osteonecrosis have been associated with HIV infection, in the absence of the classic risk factors for osteonecrosis. Metabolic risk factors include hypertriglyceridaemia. The immunological disorders that occur in the HIV infection may predispose the patient to avascular osteonecrosis and metabolic disorders, particularly hypertriglyceridemia, while the use of protease inhibitors, may be considered an additional risk factor for osteonecrosis. Given the importance of premature diagnosis and to avoid complications of osteonecrosis, we recommend evaluation of musculoskeletal symptoms in children receiving protease inhibitors.