This paper examines the relationship between choice of career and perception of the medical labor market, as well as the effects of social origin, type of medical school, and place of internship. The data are derived from a survey of interns which was conducted in Mexico during 1978, when a substantial proportion of physicians was unemployed or underemployed. Career preferences were operationalized in terms of type of activity (general practice or specialty), site (ambulatory or hospital) and institution (public assistance, social security or private). Perceptions of the medical labor market were measured as an 'objective' feasibility perception and a 'subjective' opportunity assessment. Additionally, composite indices of career preferences and perceptions were constructed in order to take account of two integrated career patterns: dominant (or majority preference) vs alternative (or minority preference). Analysis of the data consistently revealed that perception of the medical labor market had a much stronger impact on preference for alternative than for dominant career patterns. Whereas social origin had no effect on career preference, type of medical school and place of internship exhibited a statistical interaction with career preference, suggesting that certain structural conditions of the medical school and the teaching hospitals led to preference for alternative rather than dominant careers. The implications of the findings are discussed with regard to health manpower policy, to conceptions of rational career choice and to the professional status of medicine in Mexico.