ICD-11 and DSM-5 differ in the role of functional impairments for the diagnosis of a mental disorder in general. While a DSM-5 diagnosis of a mental disorder includes functional impairment as a mandatory component, ICD-11 does not.

To clarify the reasoning behind the decision of WHO not to include functional impairment as a mandatory diagnostic criterion.

To present arguments for not including functional impairment in the diagnostic criteria for mental disorders.

Presentation of con arguments.

WHO prefers functional criteria not to be included among the clinical criteria (Reed et al., 2011) and suggests using the International Classification of Functioning (ICF) to assess and code such functional impairments. Functional impairments are not always present in persons with schizophrenia, they are not disorder-specific and a WHO study has shown that their occurrence in persons with psychosis-like experiences in the general population does not inevitably indicate schizophrenia or other mental disorders (Nuevo et al., 2010).

DSM-5 will retain the mandatory criterion of functional impairment, while ICD-11 will not include it. The question of caseness with and without mandatory functional impairments in the diagnostic criteria will be one of the research issues for the upcoming ICD-11 field trials.