Mental disorders tend to be seen first in primary care settings around the world. To be helpful, classifications of mental disorders for primary care need to be simple. In response to these basic observations and requirements, a primary care version of the mental disorder section of ICD-10 has been developed by the WHO (ICD-10-PHC). This classification version has been used quite extensively internationally. The results of field trials with ICD-10-PHC are summarised here along with recommendations to make classifications and information systems more helpful to upgrade primary care of mental disorders around the world.