Mental disorders are highly prevalent and cause considerable suffering and disease burden. To compound this public
health problem, many individuals with psychiatric disorders remain untreated although effective treatments exist. We examine the
extent of this treatment gap. We reviewed community-based psychiatric epidemiology studies that used standardized diagnostic
instruments and included data on the percentage of individuals receiving care for schizophrenia and other non-affective psychotic
disorders, major depression, dysthymia, bipolar disorder, generalized anxiety disorder (GAD), panic disorder, obsessive–compulsive
disorder (OCD), and alcohol abuse or dependence. The median rates of untreated cases of these disorders were calculated across the
studies. Examples of the estimation of the treatment gap for WHO regions are also presented. Thirty-seven studies had information
on service utilization. The median treatment gap for schizophrenia, including other non-affective psychosis, was 32.2%. For other
disorders the gap was: depression, 56.3%; dysthymia, 56.0%; bipolar disorder, 50.2%; panic disorder, 55.9%; GAD, 57.5%; and
OCD, 57.3%. Alcohol abuse and dependence had the widest treatment gap at 78.1%. The treatment gap for mental disorders is
universally large, though it varies across regions. It is likely that the gap reported here is an underestimate due to the unavailability
of community-based data from developing countries where services are scarcer. To address this major public health challenge, WHO
has adopted in 2002 a global action programme that has been endorsed by the Member States.