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Resurfacing metal-on-metal hip arthroplasty is increasing in popularity, especially in younger patients. To date, studies indicate that the procedure is associated with a good outcome in the medium-term. Formation of a peri-articuar mass is a rarely reported complication. In this study we analyse the imaging findings in patients with resurfacing implants presenting to our institution with peri-articular masses identified on cross sectional imaging.All patients with documented peri-articular masses following resurfacing arthroplasty were included. The available imaging related to the masses was reviewed and the findings documented along with the patient's demographics.There were 10 patients (13 joints). All patients were female. Patients presented with periprosthetic anterior or posterolateral solid and cystic masses. The anterior masses involved psoas muscle and were predominately solid. The posterolateral masses were predominately cystic. In the three cases with bilateral arthroplasties, masses were detected in both hips. Histology in six cases showed features compatible with a type IV hypersensitivity reaction.The preponderance of females, the bilateral nature of the masses and the histological features suggest that peri-articular masses following resurfacing arthroplasty is due to the metal hypersensitivity.