The literature on the relationship between breast cancer mortality and postmenopausal oestrogen and combined oestrogen/progestin therapy is seemingly contradictory. This study explored survival after exposure to oestrogen or oestrogen plus progestin at or in the year prior to breast cancer diagnosis. Information on patients first diagnosed with invasive breast cancer between 1993 and 1998 was linked with outpatient pharmacy data from 1992 to 2000. Patients were classified according to use of oestrogen alone or oestrogen plus progestin at or in the year prior to diagnosis. Compared to nonusers, and adjusting for age at diagnosis, race/ethnicity, tumour size and grade, oestrogen receptor status, surgery status, and chemotherapy and hormone therapy for breast cancer treatment, oestrogen plus progestin users had lower all-cause mortality (stage I hazard ratio (HR) = 0.69, 95% confidence interval (CI)= 0.48-0.99; stage II HR = 0.53, 95% CI = 0.39-0.72) and breast cancer mortality (stage I HR = 0.52, 95% CI = 0.26-1.04; stage II HR = 0.69, 95% CI = 0.48-0.98). Oestrogen users experienced little or no survival benefit for all-cause mortality (stage I HR = 1.04, 95% CI = 0.77-1.42; stage II HR = 0.86, 95% CI = 0.65-1.14) or breast cancer mortality (stage I HR = 1.23, 95% CI 0.72-2.10; stage II HR = 1.01, 95% CI 0.72-1.41). Our findings suggest, relative to nonusers, a lower risk of death from all causes and from breast cancer in patients who were diagnosed with breast cancer while exposed to oestrogen plus progestin, but not in patients exposed to oestrogen only.