The current understanding that disease criteria are different than classification criteria is not well founded. In fact, they are a continuum. The arithmetic behind the two are the same and is built on a clear understanding of the concepts of sensitivity and specificity. Diagnosis is nothing different than classification in the individual patient. The main element that makes a set of criteria diagnostic is the pretest odds. We should question our current practice of making universal disease criteria and perhaps design criteria tailored to subspecialties.