Given the long-standing debate about the nature of the concept of disease, the objective of this study was to understand how doctors categorize a condition as a disease or not and what kind of information they use. A survey with a set of clinical vignettes was designed, and a group of physicians were asked to interpret those situations as a disease or not and to motivate their choice with a short written text. Thematic analysis of the answers resulted in four themes: the temporal dimension of a disease, reification of disease, disease as an existential condition, and disease as a motivation to action. The respondents’ interpretations were very heterogeneous, supporting the idea that physicians do not share a common prototypical concept of disease. An interpretation of these results according to a critical realist and systemic approach suggested that the doctor-patient relationship is the context able to influence the interpretation of a condition as a disease or not as the final outcome of a process in which both objective, subjective, and socially mediated elements are taken into consideration.