According to recent research on categorization, knowledge of a given category is structured in memory around key cases or clear examples, referred to as the prototypes, which capture the core meaning of the category. The purpose of this study was to establish a converging sequence of evidence concerning the internal structure of fourteen broad categories of medical disorders as stored in the long-term memories of pre-clinical medical students and experienced doctors. It was shown that the mental representation of the categories was better described by the overlapping features of the prototype view of categorization than the criterial features of the classical view. It is argued that the prototype view may help facilitate the understanding of the learning and problem-solving process in medicine.