Many gynaecologists do not currently close the peritoneum after caesarean section (CS). Recently, several studies examining adhesion formation after repeat CS appear to favour closure of the peritoneum after caesarean section. We performed a systematic review of the current available evidence with regard to the long-term outcome, mainly in terms of adhesion formation after closure versus non-closure of peritoneum during CS. We undertook a literature search between January 1995 and February 2008 using MEDLINE, Pubmed, EMBASE, Cochrane central controlled trials register and Cochrane pregnancy and childbirth group trials register. We also had searched all the references cited in the relevant studies. Both English and non-English language papers were included. Prospective studies which compared peritoneal closure versus non-closure during CS in terms of adhesion formation were included. Studies were included if they had a primary objective to examine adhesion formation in a repeat caesarean section, had a clear study design, had an adhesion scoring system, excluded patients who had adhesions in the primary caesarean section or interim surgeries after the primary caesarean section, and had no usage of anti-adhesion agents in the primary caesarean section. Retrospective studies which were performed by case-notes review alone, were excluded. Eleven studies were identified via our search strategy. Five were retrospective and six were prospective. Out of the eleven studies, three satisfied the inclusion criteria and were included (n=249); two studies were follow-ups of RCTs and one was not randomised. Out of 249 women included in the analysis, 110 had peritoneal closure during CS whereas the other 139 did not have peritoneal closure. Meta-analysis was performed using the two randomised studies plus (i) the unadjusted estimate from the non-randomised study and (ii) the reported adjusted estimate, adjusted for baseline differences in the groups. Non-closure of the peritoneum during CS resulted in a significantly increased likelihood of adhesion formation in both meta-analyses--OR (95% CI): (i) 2.60 (1.48-4.56) and (ii) 4.23 (2.06-8.69). This systematic review has demonstrated that according to current data in the literature, there is some evidence to suggest that non-closure of the peritoneum after caesarean section is associated with more adhesion formation compared to closure.