Occupational functioning of persons with mental disorders is a serious, rarely discussed problem in Polish literature. Foreign research review shows that occupational activity of persons with mental disorders seriously affects their mental functioning. It was suggested that the major way of mental health promotion was re-employment. However the risk of mental disorders (especially affective and anxiety disorders) increased with loss of some work. Despite of a healthy influence of occupational activity on the mental health among people suffering from mental disorders, the high level of unemployment in that group (higher than among people with somatic diseases) is observed. The aim of this article is to describe the problem of occupational activity of persons with mental disorders, as well as in comparison to people without mental disorders and those with somatic diseases. The relationship between mental disorders and occupational activity is shown. Psychological benefits of occupational functioning as well as difficulties at work caused by mental disorders are explained. The costs connected with mental disorders are described.