We investigated pregnancy outcome among obese women using a prospective cohort study comparing consecutive deliveries of obese and nonobese patients. Stratified analysis, using the Mantel-Haenszel technique, was done to assess the association between obesity and the risk for cesarean delivery (CD) while controlling for confounding variables. Complete data were abstracted for 376 women, of whom 21% ( N = 79) were obese. CD rate was significantly higher among obese women (32.9% versus 18.9%; P = 0.006). Maternal obesity was associated with multiparity (odds ratio [OR] 2.97, 95% confidence interval [CI] 1.27 to 6.97; P = 0.012), fertility treatments (OR 11.3, 95% CI 2.84 to 44.89; P = 0.001), insulin-treated gestational diabetes (OR 24.55, 95% CI 2.28 to 264.08; P = 0.008), and hydramnios (OR 20.46, 95% CI 2.17 to 192.89; P = 0.008). When controlling for possible confounders, the association between maternal obesity and CD remained significant (weighted OR 2.2, 95% CI 1.2 to 4.1; P = 0.018). No significant differences were noted between the groups regarding neonatal complications. Both first and second stages of labor were longer in obese women. Obesity is a risk factor for developing gestational hypertension, insulin-treated gestational diabetes, and hydramnios. Moreover, maternal obesity is an independent risk factor for CD. Additional independent risk factors for CD were fertility treatments, insulin-treated gestational diabetes, and hydramnios. However, neonatal outcome of obese women is comparable to women with normal prepregnancy body mass index.