For many laparoscopic surgical procedures, the preoperative images are taken with the patient in a different position than that in which the surgery is performed. The organ shift between positions can affect surgical image guidance, as the organ shifts can complicate image registration. In particular, for partial nephrectomy, the standard clinical approach requires supine preoperative computed tomography, while the surgery is performed in the flank position. We studied ten subjects in both supine and flank positions. Rigid registration was used to determine the relative motion of the kidneys, using the spine as a pose-independent landmark. Our results showed that the kidney can move as much as 46.5 mm as a result of a supine-to-flank change in patient position, and rotate as much as 25°. From the results, significant kidney motion occurs due to the change of patient position from supine to flank. These changes warrant further study to understand and model the patient specific motion.