Objectives: To compare age-adjusted all-cause and CVD mortality, relative to the general female population, for women registered for fertility treatment who received it and those who did not. Design: Prospective cohort study; analysis of Monash IVF clinical registries data, 1975–2018, linked with National Death Index mortality data. Participants: All women who registered for fertility treatment at Monash IVF (Melbourne, Victoria), 1 January 1975 – 1 January 2014, followed until 31 December 2018. Main outcome measures: Standardised mortality ratios (SMRs) for all-cause and CVD mortality, for women who did or did not undergo fertility treatment; SMRs stratified by area-level socio-economic disadvantage (SEIFA Index of Relative Socioeconomic Disadvantage [IRSD]) and (for women who underwent treatment), by stimulated cycle number and mean oocytes/cycle categories. Results: Of 44 149 women registered for fertility treatment, 33 520 underwent treatment (66.4%), 10 629 did not. After adjustment for age, both all-cause (SMR, 0.58; 95% CI, 0.54–0.62) and CVD mortality (SMR, 0.41; 95% CI, 0.32–0.53) were lower than for the general female population. All-cause mortality was similar for women registered with Monash IVF who did (SMR, 0.55; 95% CI, 0.50–0.60) or did not undergo fertility treatment (SMR, 0.63; 95% CI, 0.56–0.70). The SMR was lowest for both treated and untreated women in the fifth IRSD quintile (least disadvantage), but the difference was statistically significant only for untreated women. CVD mortality was lower for registered women who underwent fertility treatment (SMR, 0.29; 95% CI, 0.19–0.43) than for those who did not (SMR, 0.58; 95% CI, 0.42–0.81). Conclusion: Fertility treatment does not increase long term all-cause or CVD mortality risk. Lower mortality among women registered for fertility treatment probably reflected their lower socio-economic disadvantage.