The effect of previous irradiation of the pelvis on the survival of acetabular components inserted without cement in primary total hip arthroplasty was examined. We searched a database of 1319 patients who had been managed with a primary total hip arthroplasty with insertion of a hemispherical porous-coated acetabular component without cement. This revealed twelve hips in eleven patients who had been managed with previous irradiation of the pelvis. Three patients had died after less than one year of follow-up, leaving eight patients with nine acetabular components available for study at an average of thirty-seven months (range, seventeen to seventy-eight months) after the operation. The type of radiation as well as the fractionation, dose, and portals were reviewed to determine the exposure of the periacetabular region to radiation. Failure of the component was assessed radiographically and clinically. At the time of follow-up, three of the nine acetabular components had migrated, as seen on radiographs, and had been associated with progressive radiolucency without clinical symptoms. Thus, four of the nine acetabular components failed, at an average of twenty-five months (range, sixteen to thirty-eight months). The other five components had not failed clinically and were stable radiographically at an average of thirty-six months (range, seventeen to sixty-three months). The insertion of acetabular components without cement in a previously irradiated pelvis has a high rate of failure. However, a superior method of acetabular reconstruction in this difficult situation has yet to emerge.