The nature and amplitude of movement in the sacroiliac joint (SIJ) is still open to controversy. Whereas some authors using modern measuring techniques have reported on the range of motion in the SIJ of patients and in embalmed elderly humans, the following is a presentation of our observations related to healthy individuals between 20 and 50 years of age. Using a three-dimensional stereophotogrammetric method, the motion in the joints of 15 males and nine females was investigated with change in posture from the upright standing position. The general description of spatial motion, as obtained through the helical axis concept, has been used. For comparison of the results obtained, the motion is also specified as components of rotation about vertical, anteroposterior and transverse axes, or in horizontal, frontal and sagittal planes respectively. The average values for total rotation and translation were low, being 1.7 degrees and 0.7 mm respectively. One of the test subjects who was known to have occasional trouble with his sacroiliac joints exhibited more than 6 degrees rotation. No statistically significant differences could be demonstrated with respect to sex, age, or parturition. RELEVANCE:--No data are available in the literature on the motion of the sacroiliac joints of healthy men and women in the age group 20-50 years. Measurements were carried out with the aid of percutaneously introduced external markers, using conventional light photography. This is a definite advantage over the use of X-rays and radio-opaque markers that would probably remain implanted in the bone indefinitely. Therefore this method might also be considered for future use in clinical research involving the mobility of the SIJ in patients.