Objectives: This study examined the anticardiolipin antibodies in post-SARS (severe acute respiratory syndrome) osteonecrosis patients to investigate the etiology of post-SARS osteonecrosis, and to eventually provide valuable information for the early diagnosis of nontraumatic osteonecrosis and for the susceptible population screening. Methods: This study recruited 62 post-SARS osteonecrosis patients and 52 age- and gender-matched healthy controls. Fasting blood samples were collected from all the subjects through cubital veins. Immunoglobulins A, G and M (IgA, G and M) types of anticardiolipin antibodies were examined by enzyme-linked immunosorbent assay. The routine examinations of prothrombin time, thrombin time, prothrombin activity, and international normalized ratio were also performed. Results: There were 21 of 62 post-SARS osteonecrosis patients (33.9%) who showed at least one type of anticardiolipin antibodies. The titers of specific IgA, IgG, and IgM were 11.33 +/- 11.209 APL, 5.127 +/- 5.927 GPL, and 17.821 +/- 10.606 MPL, respectively. There were only 4 of 52 subjects in the control group (7.7%) who showed positive anticardiolipin antibody with titers of IgA at 10.702 +/- 3.126 APL, IgG at 5.184 +/- 4.780 GPL, and IgM at 14.684 +/- 5.516 MPL. There were significant differences between the 2 groups confirmed by t-Test and chi(2) test (P < 0.05), while no significant differences were observed in prothrombin time, thrombin time, prothrombin activity, and international normalized ratio results between the 2 groups. Conclusions: The incidences of anticardiolipin antibodies were increased in the post-SARS osteonecrosis patients and anticardiolipin antibodies may play a role in the pathogenesis of post-SARS osteonecrosis.