The occurrence of pseudotumours (soft tissue masses relating to the hip joint) following metal-on-metal hip resurfacing arthroplasty has been associated with higher than normal bearing wear and high serum metal ion levels although both these findings do not necessarily coexist. The purpose of this study was to examine patient activity patterns and their influence on acetabular component edge loading in a group of subjects with known serum metal ion levels. Fifteen subjects with metal-on-metal hip resurfacing arthroplasty (eight males and seven females) were recruited for motion analysis followed by computed tomography scans. They were divided into three groups based on their serum metal ion levels and the orientation of their acetabular component: well-positioned acetabular component with low metal ions, mal-positioned acetabular component with low metal ions and mal-positioned acetabular component with high ions. A combination of motion analysis, subject-specific modelling (AnyBody Modeling System, Aalborg, Denmark) and computed tomography measurements was used to calculate dynamically the contact patch-to-rim distance for each subject during gait and sit-to-stand. The contact-pitch-to-rim distance for the high ion group was significantly lower (p