OBJECTIVE: To investigate whether the relationship between socioeconomic status and breastfeeding initiation and duration changed in Australia between 1995 and 2004. DESIGN AND SETTING: Secondary analysis of data from national health surveys (NHSs) conducted by the Australian Bureau of Statistics in 1995, 2001 and 2004-05. The Socio-Economic Indexes for Areas (SEIFA) classification was used as a measure of socioeconomic status. MAIN OUTCOME MEASURES: Rates of initiation of breastfeeding; rates of breastfeeding at 3, 6 and 12 months. RESULTS: Between the 1995 and 2004-05 NHSs, there was little change in overall rates of breastfeeding initiation and duration. In 2004-05, breastfeeding initiation was 87.8%, and the proportions of infants breastfeeding at 3, 6 and 12 months were 64.4%, 50.4% and 23.3%, respectively. In 1995, the odds ratio (OR) of breastfeeding at 6 months increased by an average of 13% (OR, 1.13 [95% CI, 1.07-1.19]) for each increase in SEIFA quintile; in 2001, the comparative increase was 21% (OR, 1.21 [95% CI, 1.12-1.30]); while in 2004-05, the comparative increase was 26% (OR, 1.26 [95% CI, 1.17-1.36]). Breastfeeding at 3 months and 1 year showed similar changes in ORs. There was little change in the ORs for breastfeeding initiation. CONCLUSION: Although overall duration of breastfeeding remained fairly constant in Australia between 1995 and 2004-05, the gap between the most disadvantaged and least disadvantaged families has widened considerably over this period.