The aim of this study was to identify psychosocial work characteristics associated with long sick leave in a large population of male Japanese employees in multiple workplaces. We examined various psychosocial work characteristics (job overload, job control, supervisor support, coworker support, support by family and friends, role ambiguity, role conflict, intragroup conflict and intergroup conflict) of employees in six factories at the base line. We then conducted a followup survey on the recorded long sick leaves of ≥30 continuous days taken by the employees due to any medical condition. We found 574 cases of long sick leave out of 15,531 subjects during an average 5.07-yr follow-up. The results showed that high supervisor support was significantly associated with a decrease in the hazard ratio (HR) of long sick leave after adjustment for several confounding factors (95%CI; 0.69-0.97). High role ambiguity also tended to increase HR, but without reaching significance (95%CI; 0.99-1.41). The results suggest that supervisor support in the workplace may be important to reduce long sick leave in Japanese male employees. ©2013 National Institute of Occupational Safety and Health.