In a retrospective, controlled, follow-up study of 326 women who had a primary preterm caesarean section, the risks of postoperative maternal morbidity and uterine rupture or dehiscence in subsequent pregnancies were investigated in relation to the mode of incision (classical compared with low-segment transverse incision). The classical incision was associated with a higher frequency of postpartum fever in the immediate postoperative period (16% compared with 6%, P less than 0.01). Of the 326 patients reviewed 286 (88%) were contacted for information about subsequent pregnancies. Information was obtained for 70 pregnancies subsequent to a classical caesarean section, and 71 pregnancies subsequent to a low-segment transverse caesarean section, which had continued for more than 20 weeks gestation. Of the pregnancies after the classical operation 13% had abnormal scars compared with none of those after the low-segment transverse operation (P = 0.0014). The frequency of scar dehiscence was 6% after a classical scar compared with none after a low-segment transverse scar (P = 0.0581).