I canít remember hearing the term co-morbidity being uttered by psychiatrists before 1980. I think that it was the advent of the third edition of Diagnostic and Statistical Manual (DSM) and itís more comprehensive criteria – in comparison with the DSM-II – of a greater number of disorders, that led to itís adoption into psychiatry from the broader field of medicine. If one disorder shows a greater degree of association than that left to chance, it is co-morbid with that disorder. It seems that we were hoping that our disorders, as described in 1980, would by and large be separate from others. However, one article after another appeared indicating among other things that ADHD was co-morbid with other disorders like oppositional defiant disorders, or one anxiety disorder was co-morbid with other anxiety or depressive disorders. I read many of these reports and found them to be infor­ma­tive, but through the years after so many reports of so many disorders being co-morbid with so many others, I began to have a so-what attitude.
It has been noted in every edition of the DSM starting in 1980 that there was no assumption that each category of a disorder is a discrete entity with clear boundaries from other disorders, nor that there are clear boundaries between having a disorder and not having one. Realizing these limitations can reduce the frustration and or confusion that both those who diagnose and those who are diag­nosed have with our current way of diagnosing mental conditions. It is somewhat mis­leading to talk of co-morbidity when mono-morbidity has proved to be elusive.