BACKGROUND: Physical health has been demonstrated to mediate the mental health and mortality risk association. The current study examines an alternative hypothesis that mental health mediates the effect of physical health on mortality risk. METHODS: Participants (N = 14,019; women = 91%), including eventual decedents (n = 3,752), were aged 70 years and older, and drawn from the Dynamic Analyses to Optimise Ageing (DYNOPTA) project. Participants were observed on two to four occasions, over a 10-year period. Mediation analysis compared the converse mediation of physical and mental health on mortality risk. RESULTS: For men, neither physical nor mental health was associated with mortality risk. For women, poor mental health reported only a small effect on mortality risk (Hazard Risk (HR) = 1.01; p < 0.001); more substantive was the risk of low physical health (HR = 1.04; p < 0.001). No mediation effects were observed. CONCLUSIONS: Mental health effects on mortality were fully attenuated by physical health in men, and partially so in women. Neither mental nor physical health mediated the effect of each other on mortality risk for either gender. We conclude that physical health is a stronger predictor of mortality risk than mental health.