Abstract Background Recommended systolic blood pressure targets often do not consider the relationship of low diastolic blood pressure (DBP) levels with cardiovascular disease (CVD) and all-cause mortality risk, which is especially relevant for older people with concurrent comorbidities. We examined the relationship of DBP levels to CVD and all-cause mortality in older women in the Women’s Health Initiative Long Life Study (WHI-LLS). Methods The study sample included 7,875 women (mean age: 79 years) who underwent a blood pressure measurement at an in-person home visit conducted in 2012–2013. CVD and all-cause mortality were centrally adjudicated. Hazard ratios (HRs) were obtained from adjusted Cox proportional hazards models. Results After 5 years follow-up, all-cause mortality occurred in 18.4% of women. Compared with a DBP of 80 mm Hg, the fully adjusted HR for mortality was 1.33 (95% confidence interval [CI]: 1.04–1.71) for a DBP of 50 mm Hg and 1.67 (95% CI: 1.29–2.16) for a DBP of 100 mm Hg. The HRs for CVD were 1.14 (95% CI: 0.78–1.67) for a DBP of 50 mm Hg and HR 1.50 (95% CI: 1.03–2.17) for a DBP of 100 mm Hg. The nadir DBP associated with lowest mortality risk was 72 mm Hg overall. Conclusions In older women, consideration should be given to the potential adverse effects of low and high DBP. Low DBP may serve as a risk marker. DBP target levels between 68 and 75 mm Hg may avoid higher mortality risk.