104 patients from a previous randomized controlled trial comparing metal-on-polyethylene (MoP) and metal-on-metal (MoM) bearings in total hip arthroplasty were considered for a posthoc review, of which 98 were available or eligible. A total of 93 of these patients were included. The purpose of the study was to compare the incidence of pseudotumour development between groups of this study population. The rate of elevated serum cobalt levels and functional outcome measures were also compared between groups. Overall, the MoM group was associated with a significantly higher incidence pseudotumour formation and elevated serum cobalt concentrations compared to the MoP group, though subgroup analysis based on sex indicated this finding was consistent in females, but not in males of the two groups. The functional outcome did not significantly differ between groups, and pseudotumour formation was not associated with a negative impact on functional outcome.