- Summary The present study was aimed to investigate pregnancy outcome among obese women and specifically the correlation between maternal obesity and incidence of caesarean section (CS) while controlling for the potential confounding effects of other variables associated with obesity. A population-based study was performed comparing all pregnancies of obese (maternal pre-pregnancy body mass index (BMI) of 30 kg/m2 or more) and non-obese patients, between the years 1988 and 2002. Patients with hypertensive disorders and diabetes mellitus as well as patients lacking prenatal care were excluded from the analysis. Stratified analyses, using the Mantel-Haenszel technique, and a multiple logistic regression model were performed to control for confounders. During the study period there were 126 080 deliveries meeting the inclusion criteria, of which 1769 (1.4%) occurred in obese patients. Using a multivariable analysis, the following conditions were significantly associated with maternal obesity: failure to progress during the first stage (odds ratio (OR) = 3.1; 95% confidence interval [CI] 2.5, 3.8; P < 0.001), fertility treatments (OR = 2.0; [95% CI 1.6, 2.5]; P < 0.001), previous CS (OR = 1.7; [95% CI 1.5, 1.9]; P < 0.001), malpresentations (OR = 1.4; [95% CI 1.2, 1.6]; P < 0.001), recurrent miscarriages (OR = 1.4; [95% CI 1.2, 1.7]; P < 0.001) and fetal macrosomia (OR = 1.4; [95% CI 1.2, 1.7]; P < 0.001). Higher rates of caesarean deliveries were found among obese parturients (27.8% vs. 10.8%; OR = 3.2; [95% CI 2.9, 3.5]; P < 0.001). When controlling for possible confounders, using the Mantel-Haenszel technique, the association between maternal obesity and CS remained significant. No significant differences were noted between the groups regarding perinatal complications such as perinatal mortality, congenital malformations, shoulder dystocia and low Apgar scores. In conclusion, a significant association was found between obesity and CS even after the exclusion of hypertensive disorders and diabetes mellitus. Importantly, obesity alone was not associated with adverse perinatal outcome. Obstetricians should be encouraged to allow obese patients not suffering from diabetes or hypertensive disorders an adequate trial of labour.