This chapter which is based on a ten-year longitudinal study conducted with two cohorts of octogenarians, examines downward social comparison as an adjustment mechanism and its impact on well-being during the frailty process. The cognitive and affective dimensions of well-being are both taken into consideration. Our population of analysis was made up of self-respondents, aged between 80 and 84 at baseline. Descriptive analyses and multilevel models were used to examine the links between well-being, downward social comparison and the frailty process. A paradoxically slow decline in well-being was first observed over the ten years notwithstanding the general decline in health. Further analysis showed that the decline in well-being with encroaching frailty was less marked in the case of those who applied downward social comparison than those who did not. These results demonstrate that downward social comparison is an effective adjustment mechanism even in a population which, because of its advanced age, is more and more afflicted by frailty.