Current operational systems have made psychiatric diagnosis more precise and reliable. They have also contributed, however, to the emergence of several problems which are currently being addressed in empirical studies (1). The first problem is that of the threshold for the diagnosis of mental disorder. At present, this threshold is based on the presence of a given number of symptoms (often fixed arbitrarily) and a significant degree of personal suffering or impairment of social functioning (both left to the subjective evaluation of the individual clinician). However, for some mental disorders, the existence is well documented of cases which are “sub-threshold” concerning the number of symptoms, but fulfil completely the criterion of impairment of social functioning. On the other hand, for other mental disorders, the criterion of impairment of social functioning appears to be not relevant. A second problem concerns the frequent concomitance of two or more psychiatric diagnoses (so-called “psychiatric comorbidity”). The emergence of this phenomenon is in part an artefact of some characteristics of current classification systems, such as the proliferation of diagnostic categories, the reduced number of hierarchical rules, a certain tendency to psychopathological oversimplification. The use of multiple psychiatric diagnoses in the same patient may prevent a holistic approach to the individual case and encourage an unwarranted use of polypharmacy.