Twenty-three renal allograft recipients with uncomplicated post-transplant courses were sonographically evaluated on the 3rd, 10th, 30th, and 90th post-operative day. The cortical thickness (CT), pyramidal length (PL), pyramidal width (PW), corticomedullary ratio (CMR), and medullary pyramidal index (MPI) were determined at each examination. The measurements obtained from the donor before implantation were used as the baseline. PW increased significantly in the absence of rejection and obstruction in renal allograft during the early post-transplant period. Although the MPI, and to a lesser extent the CMR, detected changes in dimensions of the medullary compartment, there was considerable intra- and inter-individual variation in their values during the post-operative period.