Although hormone replacement therapy (HRT) use has been associated with breast cancers that have better prognostic features, it is not clear whether this leads to improved survival. We studied a cohort of 4022 postmenopausal women diagnosed with breast cancer between 1993 and 2000, who attended a mammographic screening program, among whom 312 deaths subsequently occurred. Proportional hazards models were used to examine survival from breast cancer and all-causes among HRT users and non-users. The multivariate hazard ratio for HRT use was 0.64 (95% CI: 0.41-1.00) for breast cancer deaths and 0.69 (95% CI: 0.49-0.96) for all-cause mortality. This was attenuated by grade (HR 0.71; 95% CI: 0.45-1.10). HRT use at diagnosis was associated with modestly improved survival from breast cancer that appeared in part to be explained by the influence of HRT on tumour grade, although we cannot exclude the possibility of confounding by factors associated with the choice to use HRT.