How detrimental are mental disorders? One way to answer that question is to consider the effects on happiness. We analyzed a representative sample (N = 7076) of the Dutch population, who were asked how often they had felt happy during the past four weeks. Mental disorders were assessed using the Composite International Diagnostic Interview. It turns out that the lowest levels of happiness are almost the exclusive domain of people with (a history of) mental disorders. The total loss of happy life years due to mental disorders is 36,6 million for the Netherlands.