Background: Regular physical activity is associated with reduced risk of mortality in middle-aged adults; however, associations between physical activity and mortality in older people have been less well studied. The objective of this study was to compare relationships between physical activity and mortality in older women and men. Methods: The prospective cohort design involved 7080 women aged 70-75 years and 11 668 men aged 65-83 years at baseline, from two Australian cohorts - the Australian Longitudinal Study on Women's Health and the Health in Men Study. Self-reported low, moderate and vigorous intensity physical activity, sociodemographic, behavioural and health characteristics were assessed in relation to all-cause mortality from the National Death Index from 1996 to 2009; the median follow-up of 10.4 (women) and 11.5 (men) years. Results: There were 1807 (25.5%) and 4705 (40.3%) deaths in women and men, respectively. After adjustment for behavioural risk factors, demographic variables and self-reported health at baseline, there was an inverse dose - response relationship between physical activity and all-cause mortality. Compared with women and men who reported no activity, there were statistically signifi cant lower hazard ratios for women who reported any activity and for men who reported activities equivalent to at least 300 metabolic equivalent. min/week. Risk reductions were 30-50% greater in women than in men in every physical activity category. Conclusions: Physical activity is inversely associated with all-cause mortality in older men and women. The relationship is stronger in women than in men, and there are benefi ts from even low levels of activity.