The relationship between social class and substance use disorders (SUDs) is explored and compared to the relationship between SES and SUDs. Social class and SES are two different conceptualizations of socioeconomic inequality (SEI) which emanate from two different theoretical orientations in sociology. SES is commonly used in epidemiological research and is usually measured in terms of education, income or occupational prestige. Social class is less known and less used. Here, following the work of Wright et al. (Wright, E. O., Hachen, D. and Costello, C. et al. (1982) The American class structure. American Sociological Review 47, 709-726) it is measured in terms of four types of control people have in their work place: ownership, control over budget decisions, control over other workers, and control over one's own work. Data are derived from an epidemiological survey, conducted in Israel, using a two stage sampling procedure for the identification of cases. In the first stage 4914 respondents were screened with the Psychiatric Epidemiological Research Interview (PERI). In the second stage (n = 2741), those who screened positive (and a sample of the negatives) were diagnosed by psychiatrists using a structured interview that yielded diagnoses according to the Research Diagnostic Criteria (RDC). The results indicate that those who are advantaged in terms of ownership, i.e. self-employed, have higher rates of SUDs compared to employees. Furthermore, it appears that most disorders have an onset subsequent to entry into the current job, indicating that ownership plays a causal role in the onset of SUDs rather than the other way around. These results are contrasted with those of a previous report from the same study by Dohrenwend et al. (Dohrenwend, B. P., Levav, I. and Shrout, P. E. et al. (1992) Socioeconomic status and psychiatric disorders: the causation selection issue. Science 255, 946-952) which showed just the opposite association between SES and SUDs, i.e. those who are advantaged in terms of SES have lower rates of SUDs. As an explanation of these apparently conflicting results, the possibility is entertained that social class and SES represent independent causal pathways to the onset of SUDs with social class mainly related to primary SUDs and SES mainly to secondary SUDs.