Diagnosis is a pivotal tool for the work of medicine as they categorise and classify individual ailments via a generalised schema. However diagnosis is also a profoundly social act, which reflects society, its values and how it makes sense of illness and disease. Considering diagnosis critically, as well as practically, is an important job of the sociologist. This paper reviews how a social model can provide a critical tool for viewing diagnosis in the genomic era. It explores how the formulation of diagnosis, be it via genetic explanations or microbiological ones, are the product of social discovery, negotiation, and consensus.