['To determine whether breastfeeding reduced the risk of childhood obesity in the infants of a multi-ethnic cohort of women with pregestational diabetes.', 'In this retrospective cohort study, women with pregestational diabetes were mailed a questionnaire about breastfeeding and current height and weight of mothers and infants. Predictors of obesity (weight for age >85 percentile) were assessed among offspring of index pregnancies, using univariate and multivariable logistic regression.', 'Of 125 women, 81 (65%) had type 1 diabetes and 44 (35%) had type 2 diabetes. The mean age of offspring was 4.5 years. On univariate analysis, significant predictors of obesity in offspring were type 2 diabetes (odds ratio, OR 2.4, 95% confidence interval, CI 0.99-5.72); maternal body mass index (BMI)>25 (OR 4.4, 95% CI 1.4-19.4); and any breastfeeding (OR 0.22, 95% CI 0.07-0.72). After multivariable adjustment, breastfeeding (OR 0.20, 95% CI 0.06-0.69) and having an overweight/obese mother (OR 3.49, 95% CI 1.03-16.2) remained independently associated with childhood obesity.'] Does breastfeeding predict the risk of childhood obesity in a multi-ethnic cohort of women with diabetes?