Breast cancer incidence has previously been shown to be greater in women of higher socio-economic status (SES), although the picture is complex due to variations in breast cancer risk factors. We have investigated the relationship between one of the strongest risk factors, breast density, with SES in a population of 6398 post- and peri-menopausal women. Volumetric breast density was measured using QuantraTM and VolparaTM, and SES was based on the Index of Multiple Deprivation (IMD) associated with each woman’s postcode. The mean IMD score was 26.39 (SD 16.7). Our results show a weak but significant association between SES and volumetric breast density; women from more deprived areas have slightly less dense breasts. After controlling for age, BMI and HRT use the relationship remained significant for density measured by VolparaTM (gradient -0.01, p