About 45% of all pregnant women and 25% of all women postpartum suffer from pelvic girdle pain and/or low back pain (PLPP). It has been suggested that increased motion of the three joints in the pelvic ring is one of the causes of PLPP. However, in spite of the availability of high technology the relation between enlarged motion of the pelvic joints and pain remains unclear. This article presents 14 studies on this topic, of which 8 are of sufficient quality to draw conclusions. The conclusion is that, during the last months of pregnancy and the first 3 weeks after delivery, motion of the pelvic girdle joints is 32-68% larger in patients with PLPP than in healthy controls. The overlap in the range of symphyseal motion between PLPP patients and healthy controls is too large to use motion as a diagnostic tool in individual cases. The findings support the idea that enlarged motion is one of the factors that causes PLPP and justifies treatment with measures to reduce this motion.