The effects of pregnancy on patients who have idiopathic scoliosis were investigated in terms of increased risk of progression of the curve. The charts, radiographs, and other pertinent data on 355 affected women who had reached skeletal maturity (Risser Grade 4) before 1975 were reviewed and analyzed. One hundred and seventy-five patients had had at least one pregnancy each (Group A) and 180 patients had never been pregnant (Group B). The groups were comparable with regard to the treatments that they had received. After skeletal maturity was reached, the curve progressed more than 5 degrees in 25 per cent and more than 10 degrees in 10 per cent of the patients in each group. The age of the patient at the time of the first pregnancy did not influence the risk of progression, and the stability of the curve before pregnancy did not decrease the risk of its progression during pregnancy. In patients who had had a spinal fusion, progression in the unfused portion of the spine was negligible in both Group A and Group B. The presence of a pseudarthrosis did not result in progression of the curve during pregnancy. The effects of scoliosis on pregnancy and delivery were evaluated in the 175 women in Group A. No specific problems that were directly related to the scoliosis were noted except for four patients, in whom delivery posed difficulties. The incidence of cesarean section was one-half of the national average, and no sections were directly related to the mother's scoliosis.(ABSTRACT TRUNCATED AT 250 WORDS)