Sleep deprivation has been shown to be associated with an increase in inflammatory makers such as interleukin-6 and C-reactive protein. The purpose of the present study was to investigate the relation between subjective poor sleep and white blood cell (WBC) count, an inflammatory marker. The subjects were 208 male Japanese workers in a synthetic fiber-manufacturing plant, who responded to a cross-sectional survey of a questionnaire on basic attributes, life style, and sleep. All male workers in the plant took an annual health checkup. WBC count was also examined in the checkup. The WBC count was greater in shift workers than in daytime workers. Shift workers complained of poor sleep more frequently, though their sleeping hours were longer. Multiple regression analysis showed that poor sleep as well as smoking habit, BMI and age were independent factors for an increase in WBC count, while sleeping hours and work pattern (shift work) were not significant factors. The present finding that poor sleep was associated with higher WBC count in male workers might suggest the importance of quality of sleep, particularly among shift workers.