OBJECTIVE: The aim of this study was to investigate the effect of gestation on initiation and duration of breastfeeding in Australian infants. METHODS: The Longitudinal Study of Australian Children recruited a national sample of children born between March 2003 and February 2004 (n = 3600 in this multivariate sample). RESULTS: Breastfeeding initiation was lower for infants of 35-36 weeks' gestation (88.2%) than 37-39 weeks' gestation (92.0%) and > or =40 weeks' gestation (93.9%). At 6 months, 41.2% of infants 35-36 weeks' gestation were breastfeeding compared with 54.5% of 37-39 weeks' gestation infants and 60.5% of infants born > or =40 weeks. Compared with infants born > or =40 weeks, infants born at 35-36 weeks had an adjusted odds ratio (OR) of 0.51 (95% CI 0.34 to 0.76) and infants born at 37-39 weeks had an adjusted OR of 0.80 (95% CI 0.69 to 0.93) of breastfeeding at 6 months. CONCLUSION: Infants born before 40 weeks are at greater risk of being artificially fed than infants born > or =40 weeks.