The relationship between social class and mental disorders, especially schizophrenia, is again and again taken for granted. It is mostly supposed that there is a causal relationship between subordinate social positions and greater prevalence of mental problems. There is, however, no apparent agreement about the concept of social class. In addition, apart from a few exceptions no sound theoretical models are available. Results of research lead to the conclusion that the relationship is complex. Moreover, some results point in the direction of a premorbid vulnerability. In the present paper this is illustrated on the basis of a follow-up study on a cohort of 83 patients with a first life-time episode of schizophrenia. It is concluded that results favour the social selection theory as opposed to social causation.