Diversity has become a buzzword in medical care, denoting a re‐evaluation of what it means to attend to differences among human bodies and lives. Questions about what types of differences matter and how they should be defined have become important normative and analytical challenges. Drawing on two case studies, we show how differences between patients and patient‐collectives are not simply waiting to be recognised and addressed but also enacted within situated healthcare practices. Although concerns with diversity are present in both cases, they take different forms. In a Viennese health–promotion project for obese clients, care practices are both based on and reproduce large‐scale categories that divide the population into distinct subgroups with specific needs. Conversely, in an outpatient clinic for bariatric surgery patients, a technical fix‐oriented procedure leads to concerns over diversity becoming an add‐on realised by tending to each patient's idiosyncrasies and personal stories. By tracing the practices of diversity and the tensions they produce, we show how classifications and understandings of human difference are based on infrastructures that enable and constrain them. Furthermore, we discuss how they become consequential in healthcare, thereby indicating the importance of remaining reflexive about the political implications of diversity discourse and practice.