Metal-on-metal (MOM) bearings with large head diameter are commonly used for total hip arthroplasty (THA). They provide low wear and a reduced risk of dislocation. Since 2001, we have done 1327 primary THAs using this bearing surface. Using revision as an endpoint, survivorship is 94% at 8 years. Of the 17 revisions (1.3%), none have been for dislocation. Five patients (0.3%) have shown evidence of a local reaction to the MOM bearing which contributed to their failure and ultimate revision. All 5 presented with elevated inflammatory indexes and had a purulent-appearing joint effusion at revision. Two showed a necrotic periarticular tissue mass (pseudotumor). The presumed diagnosis of infection and the delay in diagnosis of reaction to the MOM with pathology complicated management.