Pelvic girdle relaxation is physiologic during pregnancy and is caused by hormonal and biomechanical factors. When a pregnant women presents herself as a patient with low back- and pelvic pain, walking dysfunction, and when the pain is reproduced by sacroiliac provocation tests, the diagnosis "symptom-giving pelvic girdle relaxation" may be justified. If the same symptoms and signs continue after delivery, we suggest the term "pelvic joint syndrome". Studies of selected patients indicate an incidence of 1.5 to 16%. In a random Norwegian population comprising 1,045 women, 25% claimed to have had pelvic girdle relaxation pre- and/or post partum. Four months post partum a point prevalence of 26.5% was found to have pelvic and low back pain. One of three was diagnosed as pelvic joint syndrome on the basis of special criteria after having excluded other diagnoses by clinical examination, X-ray and laboratory controls. Symptomatic lowback pain may be a difficult differential diagnosis. Risk factors for pelvic joint syndrome seem to be previous pelvic girdle relaxation or pelvic girdle relaxation in mother and sisters.