Aggressive granulomatous lesions in cementless total hip arthroplasty. We describe six patients with aggressive granulomatous lesions around cementless total hip prostheses. Two patients previously had a cemented prosthesis in the same hip. The Lord prosthesis was used in five patients, the PCA in one. Both prostheses were made of chrome-cobalt alloy. Pain on weight-bearing occurred on average 3.2 years after the cementless arthroplasty, and at that time radiography revealed aggressive granulomatosis around the proximal femoral stem and the acetabular component in five of the patients; one had a large solitary granuloma in the proximal femur. Revision was performed on average 4.8 years after the cementless arthroplasty. At that time all granulomas had grown large in size; while waiting for revision operation, two femoral stem components fractured. All the granulomas showed a uniform histopathology, which included histiocytosis; the cause for these lesions was thought to be plastic debris from the acetabular socket. 