Background: Stigma can be a barrier for workers experiencing a mental illness to access accommodations at work. However, work accommodations may be necessary to maintain a worker's ability to work. Therefore, it may be important to develop effective interventions to address workplace stigma. Objective: To determine (1) what proportion of workers would probably disclose their mental health issue to their manager, (2) what are the motivating factors for the decision of whether or not to disclose, and (3) what would potentially change the disclosure decision? Methods: A link to a Web-based questionnaire was sent to a nationally representative sample of 1671 Dutch adults over 18 years of age. The response rate was 74%. We focused on the 892 respondents who indicated they were either employed for pay or looking for employment, not in management positions, and never experienced a mental health issue. This group comprised 73% of the total sample. They were asked if they would disclose their mental health issue to their manager. For what reasons would they disclose/not disclose the issue? And, what could change their decision? Results: We found that almost 75% of workers would disclose to their managers. The perceived relationship with their managers and feelings of responsibility to their workplaces were important contributors to the decision. A large minority of workers would not tell, preferring to deal with their issues alone. In addition, a significant proportion of workers would choose not to disclose fearing negative consequences. Conclusion: Our results indicate that the majority of these Dutch workers would disclose a mental health issue to their managers. The relationship with the manager plays a central role. The advice from a trusted individual and the experiences of colleagues are also significant factors in the disclosure decision.