OBJECTIVES: The purpose of this study was to examine daytime sleepiness-related factors, including sleeping patterns and daytime activities, in shift and non-shift workers. METHODS: One hundred and twenty two shift workers, and two hundred and fifty four non-shift workers, were selected and identified in terms of their general characteristics, such as age, tenure, educational level, marital status and religion. Screening questionnaires were composed of the Epworth Sleepiness Scale (ESS) for evaluation of daytime sleepiness, the Multidimensional Fatigue Scale (MFS) for fatigue, and the Korean version of the National Institute for Occupational Safety and Health (NIOSH) for sleeping patterns. RESULTS: The shift worker group reported significantly higher rates of sleep disturbance and higher fatigue scores compared with the non-shift workers (all p<0.01). The prevalence of daytime sleepiness was higher in the shift workers (19.7%) than the non-shift workers (10.6%) (p<0.05). The significant daytime sleepiness-related factors were found to be shift work, tenure and difficulties in falling back to sleep once woken (p<0.05). Shift work was proved to be an important factor in workers aged less than 40 years (p<0.05). However, this association was not evident in workers aged 40 years and over. CONCLUSIONS: The shift workers showed a significantly higher prevalence of daytime sleepiness compared with the non-shift workers. The present study suggests a need for the implementation of sleeping and fatigue management programs for shift workers in order to improve working efficiency and control safety accidents during shift work.