Metal-on-metal (MoM) bearings in total hip arthroplasties and hip resurfacing arthroplasties have recently shown a new type of complication: adverse reactions to metal debris (ARMD). ARMD is characterized by local severe inflammation and tissue necrosis leading to implant failures. The gluteal muscle region is important for the patient outcome after revision surgery. This prospective positron emission tomography/computed tomography (PET/CT) study was undertaken to evaluate the characteristics of 2-deoxy-2-[18F]fluoro-D-glucose ([18F]FDG) and [68Ga]Gallium citrate ([68Ga]Citrate) PET/CT in ARMD patients. [18F]FDG and [68Ga]Citrate PET/CT were performed in 18 hip arthroplasty patients: 12 ARMD patients (with 16 MoM hips) and six arthroplasty controls without ARMD. Tracer uptake was evaluated visually, and maximum standardized uptake (SUVmax) was measured in the gluteal muscle region. ARMD severity was graded by metal artefact reduction sequence-magnetic resonance imaging (MARS-MRI). Periprosthetic [18F]FDG uptake was observed in 15 of 16 hips, [68Ga]Citrate uptake in three of 16 hips, respectively. The distribution of tracer uptake resembled infection in three hips. In the gluteal muscle region, the SUVmax of [18F]FDG was significantly greater in hips with moderate and severe ARMD compared with the controls (P = 0·009 for [18F]FDG and P = 0·217 for [68Ga]Citrate). In patients who needed revision surgery, an intraoperative finding of gluteal muscle necrosis was associated with increased local SUVmax as detected by preoperative [18F]FDG (P = 0·039), but not by [68Ga]Citrate (P = 0·301). In conclusion, the inflammatory reaction to metal debris in hip arthroplasty patients is best visualized with [18F]FDG.