Background: The literature suggests that many health professionals hold stigmatising attitudes towards those with mental illness and that this impacts on patient care. Little attention has been given to how these attitudes affect colleagues with a mental illness. Current research demonstrates that stigma and discrimination are common in the UK workplace and impact on one's decision to disclose mental illness. Aims: This study aims to explore health professionals' experiences of and attitudes towards mental illness and disclosure in the workplace. Methods: This qualitative study involved semi-structured interviews with 24 health professionals employed by an NHS (National Health Service) trust. 13 of these worked in mental health, and 11 in other health fields. Interviews were transcribed and thematic analysis was used to identify themes. Results: Five key themes were identified from the data: personal experiences and their effect in changing attitudes; perceived stigmatising views of mental illness in other staff members; hypothetical disclosure: factors affecting one's decision; attitudes towards disclosure; support in the workplace after disclosure; and, applying only to those working outside of the mental health field, mental illness is not talked about. The results indicated that participants had a great deal of experience with colleagues with a mental illness and that support in the workplace for such illnesses is variable. Attitudes of participating health professionals towards colleagues with a mental illness appeared to be positive, however, they did report that other colleagues held negative attitudes. Deciding to disclose a mental illness was a carefully thought out decision with a number of advantages and disadvantages noted. In particular, it was found that health professionals' fear stigma and discrimination from colleagues and that this would dissuade participants from disclosing a mental illness. Conclusion: In many respects, this research supports the findings in other workplaces. Such findings need to be investigated further to identify the degree to which these experiences and attitudes can be applied to other health professionals in other healthcare settings to determine what intervention is necessary. Importantly, this study has also indicated that the level of support available to NHS health professionals with a mental illness is variable, suggesting the need to identify and replicate positive practice.