Objectives To elucidate sociodemographic, lifestyle, psychological, and physical factors associated with two subtypes of insomnia in Japanese male workers.Design A cross-sectional study using the annual health examination database of a Japanese company.Setting N/AParticipants Middle-aged male participants in the 1998 health examination at an employee health management center of a Japanese company (n=22, 185) .Main outcome measures Self-reported insomnia, including difficulty initiating sleep (DIS) and difficulty maintaining sleep (DMS) .Results In the young age (<45 years old) group: Significant higher odds ratio (OR) for DIS was found in living alone, shift work, smoking, lack of having three meals, psychological problems, and hypertension, with significant lower OR in overtime work and alcohol drinking. Significant higher OR for DMS was found in living alone, alcohol drinking, psychological problems, and hypertension, with significant lower OR in overtime work. In the old age (≥45 years old) group: Significant higher OR for DIS was found in living alone, smoking, lack of having three meals, lack of exercise, and psychological problems, with significant lower OR in overtime work, alcohol drinking, and hypertension. Significant higher OR for DMS was found in alcohol drinking, lack of walk, psychological problems, and diabetes, with significant lower OR in overtime work and smoking.Conclusions Insomnia was associated with psychological and physical problems, besides lifestyles, in Japanese male workers.