The statistics published by CNAV since the early 1960s show three phases of change in terms of flows of pensions granted for inability to work due to medical reasons, as well as sharp disparities between men and women: initially uncommon, particularly among women, disability retirement boomed and evened out between the sexes in the 1970s, then, since the 1980s became overwhelmingly a benefit awarded to women. By comparing CNAV’s yearly statistics with the career paths of three cohorts of salaried employees born ten years apart in the early decades of the 20th century, this paper seeks to show the malleability of the concept and the sociological profile of disability retirement as well as the reasons for gender inequality in the population of disability retirees. An analysis of the concept of “inability to work” through the prism of the job market, public policy and the career paths and medical histories of the men and women concerned sheds light on its changing profile and highlights the permanent function of disability retirement, which is to siphon off the most disadvantaged individuals of each generation. In this selection process, the egalitarian principle that prompts the legislator to ignore the specific features of women’s careers appears to be a decisive factor in the gender inequality of disability retirement.