Nine porous-coated acetabular components were retrieved post mortem. All components had been inserted at our institution and had been in situ for a mean of fifty months (range, seventeen to eighty-seven months). Clinical records revealed that all had been functioning well at the time of death, and clinical radiographs showed signs that all had been stable. Standard backscattered scanning electron microscopy was used to quantitate the amount of bone ingrowth into the porous coating. For each component, the histological appearance of the bone-metal interface was compared with the appearance on clinical radiographs. Light microscopy was used to study the non-ossified areas. Every component had growth of bone into the porous coating, with the ingrowth occupying a mean of 32 per cent (range, 3 to 84 per cent) of the fields that were examined. In areas where bone ingrowth had occurred, the mean area density was 48 per cent (range, 26 to 65 per cent). Use of radiographs consistently led to an underestimation of the presence of gap areas and an overestimation of the occurrence of bone apposition. When fibrous tissue was present in non-ossified areas, it was extremely dense and well organized. Within the limits of light microscopic examination, there was no evidence of granulomatous formation in the non-ossified regions. This is particularly encouraging since the fibrous tissue-bone interfaces seem to prohibit the deposit of particulate debris.