A cross-sectional study carried out in a Brazilian petrochemical plant aimed to examine the working conditions, work organization, and effects caused by combinations of multiple stressors. The workers completed a comprehensive questionnaire and self-assessed their working conditions (general and specific risks), sick leaves, drinking and smoking habits, sleep disturbances, diagnosed diseases, symptoms and complaints, personal availability for use of health care services, and social and family effects. A sample of 104 day and 87 three-shift continuous rotating shiftworkers was chosen from a population of 1035 workers, stratified according to age and time on the job. The sample was located in four working areas: administrative management, maintenance, industrial engineering and technical management, and operational workers. Self-ratings between day and shiftworkers indicated heavier stressors and greater strain for shiftworkers than dayworkers for most of the variables studied. Multiple comparisons were made of stress and strain between working areas, and within each area for day and shiftworkers. Results indicated general and specific risks significantly greater for shiftworkers in the operational areas. Some of the health, social and family effects were also self-assessed as more negative for shiftworkers, in all areas. Regression analysis indicated that working shifts is one important variable influencing the health and well-being of these workers.