Terminal decline in well-being is well established. However, the examination of covarying physical health and functioning on mortality-related well-being decline is limited. This study tested the effect of physical health changes on mortality-related well-being decline and examined the extent to which mortality-related trajectories of different well-being dimensions are similar. Participants comprised 1,862 decedent Australian females (aged M = 69.59 years; SD = 8.08 years at baseline) from the Dynamic Analyses to Optimize Ageing (DYNOPTA) Study who were observed on up to 4 occasions for up to 16 years (M = 6.04 years; SD = 2.14 years) prior to death, and who provided data on 2 well-being indices, vitality and mental health. Although between and within-person change in physical health fully accounted for mortality-related well-being decline, further analysis indicated that prior level of physical health reported only small effects on subsequent level of well-being and was wholly unrelated to well-being change. Conversely, only prior vitality reported significant effects on the level of, and change in, physical health. In conclusion, terminal decline in vitality and mental health appears to be an artifact of within-person physical health change and not prior level of physical health. Future areas of research should focus on identifying other significant predictors of physical health change which subsequently impact on well-being decline. There is also a need to discriminate between different indices of well-being as mortality-related changes and associations with physical function are not consistent.