We evaluated the microstructural characteristics of newly formed bone tissue at the interface with cement. The bone‐cement interfaces of the femoral components of nine hip prostheses retrieved after loosening were investigated by means of X‐ray diffraction on microareas and microhardness. The bone far from the interface of two stable prostheses was used as a control. The newly formed bone adjacent to cement in the loosened prostheses showed a maturity degree lower than that of bone adjacent to cement in stable prostheses. The lattice parameters of bone apatite did not show significant variations as compared to the reference values. Bone trabeculae at the interface with loosened prostheses often showed an osteoid lining characterized by a strongly demineralized lamellar and haversian structure. Radioopaque cement particles are sometimes found in the trabecular bone tissue around the prosthesis. © 1995 John Wiley & Sons, Inc. Copyright © 1995 John Wiley & Sons, Inc.