Significant problems have plagued medical and musicological researchers who wish to understand the complexities of Beethoven’s physical and mental health. The most significant is a lack of detailed information on the composer’s medical and mental conditions as they appeared and progressed. Though he consistently saw well-regarded doctors from around 1800 to his death, only one wrote a detailed description and only a few left information in the conversation books. Other problems are the limited medical knowledge about certain diseases at the time (such as the causes of deafness) and treatments with no or limited effectiveness (both for deafness and liver disease, for instance). Two additional problems are the focus of this essay. The first is the fact that studying the composer’s health and diseases is a cross-disciplinary endeavor that requires specialized knowledge both of medical science and of musicological expertise into every corner of Beethoven’s biography. The second concerns acquiring a knowledge of all the available sources that have survived to document the composer’s health and a critical assessment of their value.