Pseudotumor formation after hip arthroplasty is a rare complication that can occur with various head-liner articulation couples. Adverse local tissue reactions and pseudotumors have been shown to present as prosthetic infections or implant failures with a broad array of laboratory and imaging findings. We report a case of pseudotumor formation resulting from modular neckstem corrosion in a well-fixed ceramic-on-polyethylene total hip arthroplasty. The patient underwent successful revision surgery using an extended trochanteric osteotomy, long-stem revision femoral component, and headliner exchange. It is critical that surgeons are aware of the potential complications with increased component modularity and the possibility of adverse local tissue reactions resulting from fretting and crevice corrosion at modular junctions.