The paper contributes to contemporary understandings of vulnerability by expanding their scope with an understanding of vulnerability as generated through institutionalised practices. The argument draws on experiential accounts of navigating the practices of diagnosis by people living with multiple conditions of ill-health and disability. Vulnerability as a concept is used widely across different domains and conveys a multitude of meanings. Contemporary biomedicine, and its associated health systems and services, understands vulnerability mostly as inherent to particular physical and mental bodily conditions that put people at risk of ill-health or emotionally fragility. This may combine with a more epidemiological understanding of vulnerability as the experience of certain population groups subject to entrenched structural inequalities. Philosophers and feminists have argued that vulnerability is a universal experience of being human while political commentators have explored its potential as a resource for resistance and action. Diagnosis within medicine and psychiatry has been the subject of extensive social analysis, critique and activism. The paper draws on first-hand experiential accounts collected through face-to-face interviews with people living with multiple conditions about their experiences of diagnosis, mostly at the primary care level. We identify five aspects to diagnostic practice that are harmful and exacerbate the experience of vulnerability: temporal sequencing; diagnostic authority; medical specialisation; strategic symptom selection; medical isolation. However, these diagnostic practices are not best understood only in terms of the power asymmetries inherent to the medical consultation, but are embedded into the very institution of diagnosis. The paper thus proposes a combined approach to vulnerability that recognises it as a universal condition of humanity but one that becomes animated or amplified for some bodies, through their own inherent incapacities or the external structures of inequality, and through the practices of medicine as situated in particular times and places.