['An association between high prepregnant body mass index (BMI) and early termination of breastfeeding has been observed, but this finding may have depended on the sociocultural context.', 'The objective was to determine whether this association was stronger with increasing maternal obesity, was modified by gestational weight gain, and still existed when there was greater social support for breastfeeding.', 'Study participants (37 459 women) were drawn from the Danish National Birth Cohort. The association of prepregnant BMI and gestational weight gain with the termination of full or any breastfeeding by 1, 16, or 20 wk postpartum was assessed with logistic regression analyses, and the risk of early termination of full and any breastfeeding during the first 18 mo postpartum was assessed with Poisson regression analyses.', 'The risk of early termination of any (with similar results for full) breastfeeding rose progressively with increasing prepregnant BMI values (in kg/m(2)), from 1.12 (95% CI: 1.09, 1.16) for overweight (BMI = 25.0-29.9) women to 1.39 (95% CI: 1.19, 1.63) for obese class III women (BMI >or= 40) compared with normal-BMI women. Gestational weight gain did not add to or modify the association between prepregnant BMI and breastfeeding.'] Is high prepregnant body mass index associated with early termination of full and any breastfeeding in Danish women?