Caesarean section is a common major surgical procedure and long-term complications have not been fully investigated. By longitudinal population based register studies, based on National health registers and medical data records, maternal complications after caesarean delivery at subsequent labour (N=7 683), among extremely preterm births (N=406), and at remote gynaecologic surgery (N=25 354) were explored. In Paper I, uterine closure was investigated in respect to uterine rupture in a subsequent delivery after caesarean section. Uterine rupture occurred in 1.3 % of women with a previous caesarean section. There was no increased risk of uterine rupture with single compared with double layers for closure of the uterus (adjusted Odds Ratio 1.17, 95 % CI 0.78-1.70). Modifiable risk factors of uterine rupture in a trial of labour after caesarean section included induction of labour and use of epidural analgesia. In Paper II, maternal outcomes and surgical aspects of caesarean section in the extremely preterm period were assessed. Maternal complications were more frequently reported in extremely preterm- compared with term caesarean delivery. No increase in short-term morbidity was observed at 22-24 compared with 25-27 gestational weeks, but uterine corporal incisions were performed more frequently (18.1 % vs. 9.6 %, p=0.02). Furthermore, risk factors for abdominal adhesions after caesarean section and organ injury in remote gynaecologic surgery were analysed (Paper III and IV). Numbers of prior caesarean sections were the most important factor for formation of adhesions. Advanced maternal age, obesity, infection and delivery year 1997-2013 were factors associated with adhesions in conjunction with caesarean section. Organ injury occurred in 2.2 % of women undergoing benign hysterectomy. A history of caesarean section increased the risk (adjusted Odds Ratio 1.74, 95 % CI 1.41-2.15), but was only partly explained by the presence of adhesions. The organ affected depended on medical history; prior caesarean predisposed for bladder injury, prior bowel/pelvic surgery for bowel injury and endometriosis was associated with ureter injury at time of hysterectomy. In conclusion; data from National health registers indicates that caesarean delivery is associated with long-term complications, although the absolute risk of severe complications for the woman is low.