Depression is a major illness with health and social effects similar to those for chronic diseases like hypertension, congestive heart failure or diabetes. The Global Burden of Disease Programme of WHO indicates that depressive disorders are among the most important causes of death and disability in both developing and industrialized countries. However, there are wide variations in its prevalence and incidence among countries, perhaps partially due to different definitions, diagnostic measures and thresholds. In western Europe, major depression affects between 5% and 10% of the populations.