Objective:  This study was undertaken to examine whether there is a protective effect of grand multiparity on the risks of death from hormone‐dependent cancers.
Methods:  The study cohort consisted of 144 922 women with at least five children (grand multiparous (GM) women) in the Birth Register between 1 January 1978 and 31 December 1987. Standardised mortality ratios (SMRs) for cancers of the breast, endometrium and ovary were calculated by dividing the numbers of observed cancer deaths to the expected numbers of deaths based on the rates of national female population.
Results:  Among the 144 922 GM women, a total of 394, 18 and 72 deaths were caused by cancers of the breast, endometrium and ovary, respectively. The SMRs among GM women were 0.73 (95% confidence intervals (CI) 0.66–0.80) for breast cancer, 0.54 (95% CI 0.29–0.79) for endometrial cancer and 0.64 (95% CI 0.49–0.79) for ovarian cancer.
Conclusions:  This study provides evidence that grand multiparity may confer a protective effect on the risk of death from cancers of the breast, endometrium and ovary.