This paper presents a new method for registering computer tomography (CT) volumetric data of human bone structures relative to observations made at different times. The system we advance was tested with different kinds of CT data sets. In this paper we report on some representative experimental results obtained with the CT data of the hip bones of a patient prior to and after prosthetic surgery aimed at the reconstruction of the hip articulation. The method works with rigid data having arbitrary relative position and orientation and proves to be robust with respect to CT acquisition noise and with respect to the segmentation technique adopted to select the region of interest for registration. The method is capable of registering correctly data sets taken from the same articulation and whose components have undergone small relative displacements. The method is also amenable to registration of heteregeneous kinds of volumetric data, e.g., CT scans and Magnetic Resonance Imagery (MRI) scans, which show different characteristics in correspondence to the same organic structure.