OBJECTIVE: To compare breast cancer incidence in England and Australia by age, extent of disease and deprivation. METHODS: We analysed data for women aged 15-99 years diagnosed with breast cancer in England or Australia during the period 1990 to 1994, and in West Midlands or New South Wales during the period 1980 to 2002. We calculated three-year rolling average incidence rates and incidence rate ratios (IRR) between West Midlands and New South Wales by age, extent of disease and category of deprivation. RESULTS: Breast cancer incidence was higher in England than in Australia, and in West Midlands than in New South Wales but became more similar over time. Socio-economic differences in incidence were greater in New South Wales than in West Midlands. The most deprived women in West Midlands were diagnosed at a later stage of disease than the most deprived women in New South Wales. Incidence among elderly women was higher in West Midlands than in New South Wales. There were also high proportions of tumours with unknown stage among elderly women in West Midlands. CONCLUSIONS: Although the overall incidence of breast cancer is similar, differences by age, extent of disease and deprivation exist. IMPLICATIONS: The underlying reasons for these patterns require further examination.