OBJECTIVE: To investigate differences in breast cancer prognostic factors between ethnic and socioeconomic groups in New Zealand. METHODS: We analyzed all 21,586 breast cancer cases on the New Zealand Cancer Registry (July 1994-June 2004). Māori, Pacific, and non-Māori/non-Pacific women were categorized according to ethnicity on the Registry. Deprivation was analyzed as quintiles of the New Zealand Deprivation Index 2001, an area-based measure of socioeconomic position. Logistic regression was used to estimate age-adjusted odds ratios (OR) (95% confidence intervals (CI)). RESULTS: Māori and Pacific women were more likely to have non-local stage, less well differentiated cancer, larger tumors and positive human epidermal growth factor receptor-type 2 (HER-2) status than non-Māori/non-Pacific women. Māori were less likely and Pacific women more likely than non-Māori/non-Pacific women to have negative oestrogen (ER) and progesterone receptor (PR) status. Adjusting for deprivation did not materially alter the results. Women living in more deprived areas had a higher risk of non-local stage and larger tumors. These associations were only partially explained by ethnicity. There was no relationship between tumor grade, ER, PR or HER-2 status and deprivation. CONCLUSIONS: Our results confirm that Māori, Pacific and low socioeconomic women present with poor prognosis breast tumors.