International audience ; There seem to be socioeconomically differences in survival for females with breast cancer, usually associated with a higher stage of disease. However, differences within tumor size have not been studied. Aim of this study is to assess differences in survival according to socioeconomic status (SES), stratified for tumor size and stage at diagnosis, for females with breast cancer in the Netherlands. All females diagnosed with breast cancer (1995-2005) were selected from the Netherlands Cancer Registry. Patients were linked to a SES database according to postal code. A multivariable logistic regression was used to assess factors associated with SES. Overall survival (OS) and relative survival (RS) were calculated. Overall, 127,599 patients were included. Higher SES was associated with lower T-stage ( < 0.0001). A decreased survival (OS and RS) was found for patients with a lower SES. Also within different size groups, RS was different. Overall, 10-year OS for the high SES group was 65 and 58% for the low SES group (hazard ratio 1.1, < 0.001) and RS was 79 versus 74% (relative excess risk, RER 1.2; < 0.001). The socioeconomic differences remained statistically significant ( < 0.001) after adjustment for age, year of diagnosis, grade, TNM stage, and treatment. For the lowest SES group 777 deaths could be avoided. Socioeconomic differences in survival of breast cancer patients were observed in the Netherlands. Higher stage at diagnosis of patients with a lower SES only partly explains the decreased survival. Policies aimed at the reduction of socioeconomic health inequalities might be important to improve survival of breast cancer.