Objectives In the elderly, the risk of mortality because of physical illnesses related to anxiety disorders varies with potential confounding influences, including comorbidity with depressive disorders. Our study aimed to explore (i) whether anxiety disorders increase the risk of mortality in the elderly, and (ii) whether the risk of mortality mediated by anxiety and depressive disorders differs between physical illnesses. Methods Our longitudinal cohort study included subjects aged over 60 years from the National Health Insurance Research Database. One thousand and eighty‐six subjects with anxiety disorders and 50 554 control subjects without anxiety disorders were included. Propensity score‐matched cohorts were analyzed. Rate ratios (RRs) were calculated for the risk of mortality associated with different physical illnesses with comorbidities of either anxiety disorders only or both anxiety and depressive disorders. Results The risk of mortality in patients with anxiety disorders was significantly higher than controls, and was even higher when subjects had both anxiety and depressive disorder comorbidities. Furthermore, the co‐occurrence of anxiety and depressive disorders increased the risk of mortality in elderly patients with ischemic heart diseases (RR = 1.60; 95% CI: 1.14–2.24). Conclusions Coexisting anxiety and depressive disorders could increase the risk of mortality in elderly patients with ischemic heart diseases. Copyright © 2016 John Wiley & Sons, Ltd.