Although the difficulty of applying psychiatric classifications to primary care has been widely criticized, there have been few investigations up to now to define and systematize the real demands in regards to these nosological systems. Recently, the revised version of the Mental and Behavior Disorders Chapter of the ICD 10 has been published. The new tool is the result of an elaboration process mainly developed by a group of 971 primary care physicians coordinated by 55 psychiatrists. The project was organized into three phases: a) evaluation of the current version and collection of proposals for change; b) definition of objectives for an optimized version; and c) writing a proposal of revised text. The result is a text that is more assimilable to a diagnostic and therapeutic guide than a mere coding system, more adapted to the role that the primary care physician can play in each disorder, more up-dated (especially in the treatment section) and more specific in many aspects.