Inflammatory pseudotumor has been commonly reported in patients undertaking total hip replacement (THR) for different reasons. The precise etiology of this biological reaction and whether the primary disease has an influence on pseudotumor formation remain unclear. There seems to be a consensus that metal ions and debris do play an important role during this process. Recently, however, compared to metal particles along, immune response induced by metal particles attracts more attention. We present two cases of pseudotumor who have accepted THR for ankylosing spondylitis (AS) and later required revision surgery and hindquarter amputation, respectively. By thorough literature review, we tried to investigate the association between inflammatory pseudotumors and immunology.