In palaeoepidemiology the number of outcome variables that can be studied is limited by the nature of the material; of those that are available, disease is the most significant. Diagnosis is one of the three bases of clinical practice, the two others being prognosis and treatment. Two things emerge from studying the history of joint – or indeed, any other – disease. Firstly – and obviously – understanding the nature of the disease depends on notions of aetiology that prevailed at the time. Secondly, changing fashions in diagnosis often make it extremely difficult to render diagnoses made in former times into their modern equivalents. For some diseases, criteria have been developed that must be satisfied before a diagnosis can be made. When making a diagnosis from human remains, one almost always relies on the gross appearances of any abnormalities present, or – in a relatively few instances – on radiology.