Background: This study aimed to develop a new instrument for bipolar disorder screening, the Workplace Bipolar Inventory (WBI), and examine its efficiency as compared with Mood Disorder Questionnaire (MDQ) and Bipolar Spectrum Diagnostic Scale (BSDS) among workers on leave of the absence due to their mental health problems. Methods: Participants were recruited at a psychiatric outpatient clinic for return-to-work in Tokyo, Japan, during September to November 2009. 81 outpatients were recruited, 55 of whom (68%) agreed to participate in this study. Participants answered questionnaires including WBI, MDQ, BSDS, and demographic factors. Their diagnostic information according to the international statistical classification of diseases and related health problems 10th revision (ICD-10) was obtained from their attending psychiatrists. The WBI is a new self-rating 39-item questionnaire which developed with input from occupational mental health specialists and an analysis of WHO Composite International Diagnostic Interview (CIDI) items. The WBI contains 3 subtype scales: WBI-A (5 items), WBI-AB4 (9 items), and WBI-AB (39 items). Results: Reliability of these scales was moderate. In the AUC of these scales, BSDS was the best of them (0.83). In the optimal cut-off point of these scales, WBI-AB4 showed good efficiency of screening (sensitivity=0.78, specificity=0.75). Both MDQ and BSDS had high specificity, while low in sensitivity. Limitations: The well validated diagnostic method (i.e., the structured clinical interview for DSM-IV [SCID] or CIDI) was not applied in this study. Conclusions: The WBI, especially WBI-AB4 would be a useful workplace screening tool for workers with bipolar disorder.