['Obesity is epidemic worldwide, and increases in cesarean delivery rates have occurred in parallel.', 'This study aimed to determine whether cesarean delivery is a risk factor for obesity in adulthood in a birth cohort of Brazilian subjects.', 'We initiated a birth cohort study in Ribeirão Preto, southeastern Brazil, in 1978. A randomly selected sample of 2057 subjects from the original cohort was reassessed in 2002-2004. Type of delivery, birth weight, maternal smoking, and schooling were obtained after birth. The following data from subjects were collected at 23-25 y of age: body mass index (BMI; in kg/m(2)), physical activity, smoking, and income. Obesity was defined as a BMI ≥30. A Poisson multivariable model was performed to determine the association between cesarean delivery and BMI.', 'The obesity rate in adults born by cesarean delivery was 15.2% and in those born by vaginal delivery was 10.4% (P = 0.002). Adults born by cesarean delivery had an increased risk (prevalence ratio: 1.58; 95% CI: 1.23, 2.02) of obesity at adulthood after adjustments.'] Is cesarean delivery associated with an increased risk of obesity in adulthood in a Brazilian birth cohort study?