We report a case of non-Hodgkin B-cell lymphoma within the bony base of an implanted acetabular cup of a total hip arthroplasty. The diagnosis was made while revising a loose prosthesis and treatment of a non-union of a periprosthetic fracture. This case demonstrates that it is important to consider tumour development in differential diagnoses of pain originating in and around a loose prosthesis. It also illustrates the need for better understanding of the relationship between haematopoietic malignancies and possible carcinogenic effects of implant debris.