Most studies that investigate the impact of mental disorders on work performance have been conducted in Western countries, but this study examines the impact of common mental disorders on sick leave and on-the-job work performance in a community sample of Japanese workers. Data from the World Mental Health Japan survey were analyzed. A subsample of 530 workers aged 20-60. years were interviewed using the WHO Composite International Diagnostic Interview 3.0. The WHO Health and Work Performance Questionnaire, was used to assess sick days and on-the-job work performance for the previous 30. days. Linear regression was used to estimate the impact of mental disorders on these indicators of work performance over 12. months. Mood disorders, including major depressive disorder, and alcohol abuse/dependence were significantly associated with decreased on-the-job performance. There were no significant associations between mental disorders and sick/absent days. Consistent with previous studies, major depression has a great impact on on-the-job work performance in Japan. The lost productivity was estimated at approximately 28-30 lost days per year. A similar decrease in on-the-job work performance was found for alcohol abuse/dependence, which is stronger than that in other countries, probably attributable to greater tolerance of problematic drinking at Japanese worksites. © 2012 Elsevier Ltd.