OBJECTIVE: We investigated the impact of active smoking and exposure to passive smoke on the risk of developing diabetes. RESEARCH DESIGN AND METHODS: Data were analyzed from a cohort of participants in the High-Risk and Population Strategy for Occupational Health Promotion Study (HIPOP-OHP) conducted in Japan from 1999 to 2004. Active and passive smoking status in the workplace was evaluated at baseline. RESULTS: Of 6,498 participants (20.9% women), a total of 229 diabetes cases were reported over a median 3.4 years of follow-up. In the workplace, compared with zero-exposure subjects, the multivariable-adjusted hazard ratios of developing diabetes were 1.81 (95% CI 1.06-3.08, P = 0.028) for present passive subjects and 1.99 (1.29-3.04, P = 0.002) for present active smokers. CONCLUSIONS: In this cohort, exposure to passive smoke in the workplace was associated with an increased risk of diabetes after adjustment for a large number of possible confounders.