The correlation between preoperative radiographic findings and intraoperative testing for stability was evaluated for 75 cementless femoral components. Fourteen of 45 porous-coated prostheses were unstable. The following radiographic signs were correlated with instability in order of significance: radiolucent lines at the bone-prosthesis interface covering greater than 50% of the porous interface, a distal pedestal, calcar hypertrophy, poor implant-cortical contact, and varus component alignment. Signs consistent with implant stability were good implant-cortical contact, spot welds, and calcar atrophy. Preoperative radiographs have predictive value in assessing the mechanical stability of the cementless femoral component at the time of surgery.