Twenty-five patients (21 females and 4 males) with sacroiliac joint disorders were studied with roentgen stereophotogrammetry in physiologic positions as well as in the extreme of physiologic positions. There was a constant pattern of motion with different load, especially around the transverse axis. The rotations were small and in mean between extreme position 2.5° (0.8°-3.9°). The translation was, mean, 0.7 mm (0.1-1.6 mm). There was no difference between symptomatic and asymptomatic joints.