Massive osteolysis and granulomatous pseudotumor tissue reactions are long-term complications of total hip replacement. It is a condition of localized bone resorption in contact with prosthetic material. It is speculated to be a consequence of metal hypersensitivity or inflammatory reaction to excessive wear. Ten years after total cementless hip replacement (metal on polyethylene surface), a 70-year-old patient presented with hip pain and pseudotumor with massive osteolysis of proximal femur on x-ray. Intraoperatively, extensive metallosis with significantly worn metal head (316L stainless steel) and only slightly worn polyethylene insert was found. Upon extraction, parts of the affected tissue and bone that were in direct contact with the prosthesis were sent for histopathologic analysis. Microscopic examination showed necrotic soft and bone tissue, mainly bone marrow with numerous histiocytes and multinucleated giant cells containing lots of pigmented particles (presumed to be metal particles as a result of implant surface wear). In this case, the primary cause of osteolysis and granulomatosis was inflammatory reaction to metal debris. Aggressive granulomatosis has been first described in cemented prostheses and afterwards also in cementless ones. Conditions such as primary or metastatic neoplastic processes and infection should be excluded. The presence of foreign molecular particles due to wear of the prosthesis by different mediators has been presumed to cause an inflammatory reaction that leads to bone resorption and loosening of the prosthesis.