STUDY QUESTION Does exposure to menopausal hormone therapy (MHT) in mid-aged women alter their risk of cardiovascular disease (CVD) mortality and all-cause mortality SUMMARY ANSWER MHT soon after menopause is unlikely to increase the risk of CVD mortality or all-cause mortality and may have a protective effect for women with hysterectomy/oophorectomy. WHAT IS KNOWN ALREADY The balance of benefits and risks of MHT are currently unclear and may differ according to when treatment starts and whether women have an intact uterus. STUDY DESIGN, SIZE, DURATION A total of 13 715 participants from the mid-aged population-based cohort (born 1946-1951) of the Australian Longitudinal Study on Women's Health (ALSWH) were followed from 1998 to 2013. PARTICIPANTS/MATERIALS, SETTING, METHODS The measures included cardiovascular and all-cause mortality, exposure to MHT and menopausal status (based on 3-yearly self-reports). Electronic prescriptions data on MHT were also available from mid-2002 onwards. At each follow-up survey wave, participants were classified as: An existing user of MHT, an initiator of MHT or a non-initiator of MHT. MAIN RESULTS AND THE ROLE OF CHANCE After adjusting for confounding variables, existing users of MHT had a reduced risk (hazard ratio 0.63; 95% CI, 0.43-0.92) of CVD mortality compared with non-initiators. Insufficient evidence of an association was identified for initiators of MHT (0.66; 0.35-1.24). For all-cause mortality, risks were reduced for both initiators (0.69; 0.55-0.87) and existing users (0.80; 0.70-0.91). In a subgroup analysis, women with hysterectomy/oophorectomy had lower risks of CVD mortality for both initiators (0.14; 0.02-0.98) and existing users (0.55; 0.34-0.90), but no evidence of an association was found for women whose MHT commenced during or after menopause. Similarly for all-cause mortality, only the women with hysterectomy/oophorectomy had lower risks for both initiators (0.47; 0.31-0.70) and existing users (0.69; 0.58-0.82). LIMITATIONS, REASONS FOR CAUTION Limitations include the observational nature of the study, the small number of deaths, MHT use being self-reported and the classification of menopausal status also being based on self-reported information. WIDER IMPLICATIONS OF THE FINDINGS Women considering MHT soon after menopause can be reassured that the treatment is unlikely to increase their risk of CVD mortality or all-cause mortality.