OBJECTIVE: To examine the relationship between maternal obesity and the initiation and duration of breastfeeding. METHODS: Analysis was made of the 1995 National Health Survey, in which personal interviews were conducted on a multistage area sample of private dwellings and a list sample of non-private dwellings in all states and territories of Australia. Mothers between the ages of 17 and 50 years (n = 1991) with children under the age of 4 years in 1995 participated in the study. RESULTS: Of the group of mothers with a body mass index (BMI) of 20-25, 89.2% (95% confidence interval (CI) 87.4-91.0) initiated breastfeeding, compared with 82.3% (95% CI 77.6-87.0) of mothers with a BMI of 30 or more. There was also a significant difference between the mean and median duration of breastfeeding of obese and non-obese mothers (BMI 30 and over, < 25, respectively). These differences remained significant when maternal smoking, age and other sociodemographic factors were taken into consideration. CONCLUSIONS: Health professionals should be aware that obese women may be at increased risk of not breastfeeding or stopping breastfeeding prematurely.