P>Objective To investigate the relationship between avascular osteonecrosis (AVN) and corticosteroid treatment given to patients with severe acute respiratory syndrome (SARS). Methods Longitudinal study of 71 former SARS patients (mainly health care workers) who had been treated with corticosteroids, with an observation time of 36 months. Magnetic resonance images (MRI) and X-rays of hips, knees, shoulders, ankles and wrists were taken as part of the post-SARS follow-up assessments. Results Thirty-nine per cent developed AVN of the hips within 3-4 months after starting treatment. Two more cases of hip necrosis were seen after 1 year and another 11 cases of AVN were diagnosed after 3 years, one with hip necrosis and 10 with necrosis in other joints. In total, 58% of the cohort had developed AVN after 3 years of observation. The sole factor explaining AVN in the hip was the total dose of corticosteroids received. Conclusion The use of corticosteroids in SARS has been debated; opinions conflict about whether the immediate benefits in terms of saving lives compensate for the adverse effects, including AVN.