Objective. - To evaluate the association between physical activity and all-cause mortality in postmenopausal women. Design. - Prospective cohort study with 7 years of follow-up through December 31, 1992. Setting and Participants. - Subjects were 40 417 postmenopausal Iowa women, aged 55 to 69 years at baseline in 1986. Physical activity was assessed by mailed questionnaire. Main Outcome Measure. - All-cause mortality (n=2260). Results. - After adjustment for potential confounders and excluding women who reported having cancer or heart disease and those who died in the first 3 years of follow-up, women who reported regular physical activity were at significantly reduced risk of death during follow-up compared with women who did not (relative risk [RR], 0.77; 95% confidence interval [CI], 0.66-0.90). Increasing frequency of moderate physical activity was associated with reduced risk of death during follow-up (from rarely or never engaging in activity to activity at least 4 times per week, RRs, 1.0 [referent], 0.76, 0.70, and 0.62; P value for trend<.001). A similar pattern was seen for vigorous physical activity (corresponding RRs, 1.0, 0.89, 0.74, and 0.57; P value for trend=.06). Reduced risks of death with increased physical activity were evident for cardiovascular diseases (n=729) and respiratory illnesses (n=147). Women who engaged only in moderate but not vigorous physical activity also benefited, with moderate activity as infrequently as once per week demonstrating a reduced mortality risk of 0.78 (95% CI, 0.64-0.96). Conclusions. - These results demonstrate a graded, inverse association between physical activity and all-cause mortality in postmenopausal women. These findings strengthen the confidence that population recommendations to engage in regular physical activity are applicable to postmenopausal women.