In 1939, Robert Faris and Warren Dunham published their pioneering work on "Mental disorders in urban areas". They investigated the distribution of mental disorders in Chicago. In the following decades, a number of studies using a similar design were carried out in various cities in the United States and in Europe, which largely replicated Faris' and Dunham's findings. The concentration of most psychiatric disorders in certain problem areas indicates the existence of a relationship between their distribution and unfavorable social conditions. However, the intention of ecological studies to find strong evidence for the psycho-social cause of mental disorders, especially of schizophrenia, failed. In schizophrenia, social selection leading to a particular spatial distribution of schizophrenic patients as a consequence of their illness or premorbid condition seems to be the most important factor. Rather than making a substantial contribution to the search for the causes of mental disorders as has been assumed up to now, identifying high risk areas of psychiatric disorders may serve as a rational basis for service planning and the allocation of resources.