Much of the working population in developing countries are engaged in shift work now and the number of shift workers is not expected to decrease in the future mostly because the need for continuity of production is increasing. Therefore, the possible effects of shift work on health are of particular interest, and in fact, there have been many epidemiological studies on shift work since the first world war. However, no studies on health effects of shift work have been reported in Korea, and the existing studies in western world have arrived at quite different conclusions mainly because the conditions of work other than shift work, such as age and selection of workers, work environment, and labor conditions also influence the health of workers. This study was firstly carried out in Korea to investigate the health risks related to shift work with 2,093 female workers randomly selected from three major manufacturing industries in proportion to total number of female workers in those industries. Differences of work conditions other than shift work in this study were adjusted by multivariate analysis. Ma findings obtained from this study are as follows : 1. There were significant differences between shift and day workers in the distribution of age, type of industry, condition of noise and dust, regularity of mealtime, working position, and working duration. Shift workers tended to be younger, to have shorter working duration, to have more irregular mealtime, to work in standing position, and to work under more noisy and dusty environment than day workers. 2. Univariate analysis showed that shift work increased the Todai Health Index (THI) scores of digestive tract, respiratory tract, and mental instability symptom categories. Shift work also increased days of sickness absence and number of industrial accident per 100 workers per month. 3. Multivariate analysis that adjusted the differences of demographic, occupational and non-occupational health-related working conditions showed that digestive tract symptom and mental instability symptom scores were significantly higher in shift workers than those in day workers. Based on these study results, it is concluded that the shift work has significant effects on some psychophysiological conditions of the workers and the effects are also influenced by several other personal and working conditions.