Eight women with pregnancy-associated osteoporosis were studied for up to ten years. Back pain and vertebral collapse usually occurred in the first pregnancy and did not recur in two subsequent pregnancies. Except in one patient, bone histology showed no increase in resorption. Plasma concentrations of 1,25-dihydroxyvitamin D tended to be low whereas those of calcitonin were, with one exception, normal. It is suggested that in these patients there may have been a transient failure of the usual changes in calciotropic hormones to prepare the maternal skeleton for the stress of childbirth. However, subsequent pregnancies in such patients are not necessarily contraindicated.