Dave, a 52-year-old U.S. Navy veteran, suffers from post-traumatic stress disorder stemming from a difficult childhood. In his job at a government agency, raised voices during meetings triggered thoughts of his abusive father, and his social anxiety occasionally prevented him from leaving his house in the morning. He felt uncomfortable hiding his condition, but he struggled to decide whether to tell his employer about it. “I didn't have a broken arm or anything that would be easy for them to understand,” he says. “I didn't know how they would react.”

The World Health Organization reports that mental illness is among the leading causes of disability across the globe. In a 2011 survey of more than 2,000 people, about a quarter reported experiencing a mental health problem on the job, according to the Chartered Institute of Personnel and Development, a British human resources agency. In the U.S., depression alone causes employees to miss 200 million days of work every year, costing employers $31 billion in lost revenue.

Despite its prevalence, mental illness is steeped in stigma, and people who call in sick or otherwise fall behind at work because of mental health issues often fabricate excuses to cover up the real reason for their lapse. They have reasons to be wary: other people may begin to perceive them differently, and the repercussions, such as being excluded socially or passed over for assignments, could damage their careers. On the other hand, revealing a psychiatric disability entitles you to workplace adjustments—and it might even improve your mental health and your relationship with your supervisor.

A few companies are offering accommodations that help employees with mental health needs avoid challenging situations and maintain productivity. If current trends continue, more people may become comfortable revealing their emotional and cognitive limitations, to everyone's benefit. “On the one hand there is needless suffering ... but it's also costing [employers] in terms of lost productivity and absenteeism,” says Clare Miller, director of the Partnership for Workplace Mental Health. People work better and more efficiently when they feel supported, she adds.

Battling Stigma

Historically, people who have revealed their mental illness at work have faced discrimination. For instance, in a 2010 survey of U.K. employers, about 40 percent said they considered hiring someone with a mental illness to be a “significant risk” to the company. Many employers believe that people with mental illnesses are difficult to get along with and unreliable. People with mental illness may be denied promotions and other opportunities for advancement. Even in supportive office environments, employees with mental illness sometimes feel increased scrutiny from their co-workers. “There's this overshadowing, where every time someone gets unhappy or upset people start thinking, ‘Oh, maybe they're relapsing,’” says psychiatrist and mental health services researcher Claire Henderson of King's College London.

If your employer is at all sympathetic to your problem, however, talking about your illness can offer benefits. For one, it may relieve the stress that comes from hiding personal information. You can also control the timing and message; otherwise your manager, who may already have noticed something is going on, may draw his or her own conclusions.

Furthermore, the Americans with Disabilities Act (ADA), passed in 1990, prohibits discrimination in hiring and firing decisions based on physical and mental disabilities and entitles people to “reasonable accommodations” from their employers. In the case of mental disabilities, these fixes may include flexible working hours, access to a quiet area and additional feedback from supervisors. In many cases, the modifications cost little to no money and can make a big difference to employee happiness and productivity.

The ADA protections are not ironclad, however. Many managers are not familiar with the details of the law, and people who experience discrimination often lack the resources to bring their case to court, says Susan G. Goldberg, a lawyer and clinical psychologist at Duquesne University. In practice, discrimination is difficult to prove: about 90 percent of plaintiffs who bring suits under the ADA lose their cases.

Researchers suggest that employees considering broaching a mental health concern should know what they hope to gain. If your work has started to suffer, disclosing a mental illness may help you explain the situation and get assistance. On the other hand, if you are getting along fine, offering this sensitive information is probably not worth the risk.

A critical consideration is the workplace climate. You can try to gauge your employer's response ahead of time by looking for certain signs. Those with a history of hiring people from diverse backgrounds may be more understanding. But supervisors may frown on your disclosure if you hold a job with stringent requirements, such as security clearance, as was the case for Dave.

Coming Out

If you decide to share your mental health status with your boss or human resources manager, consider doing so soon—but not immediately—after being hired. In most situations, experts suggest waiting six months to a year, after you have built relationships with your employer and colleagues. But do not delay too long. Although technically the ADA allows for disclosure anytime during employment, courts have been less inclined to see the employee's side if he or she is close to getting fired, Goldberg says.

Before telling your supervisor, sketch a script for the conversation. Experts suggest first highlighting your skills and abilities and coming prepared with specific adjustments that could improve your work even more. More important, decide how much you are going to divulge. If you are not comfortable getting into specifics, you can say you have a “medical condition” that causes you to need certain accommodations and leave it at that.

Some employers have begun opening up to mental illness. JPMorgan Chase, IBM and DuPont were early adopters of progressive mental health policies. DuPont, for instance, has a program called ICU Mental Health that encourages employees to notice signs of emotional distress and reach out to co-workers who might be having problems. In 2012, the year the program started, the number of employees using mental health services grew at least 15 to 20 percent. Last year shoe company Zappos implemented a similar program, called Right Direction, aimed at raising awareness about depression. If more companies start talking about mental health issues without judgment, more employees will feel comfortable seeking out behavioral health services and accommodations, Miller says. Ultimately, she adds, the changes would decrease disability costs and turnover.

But the progress is uneven. Although the stigma of mental illness has lifted in some quarters, “I don't think it has changed for the vast majority of people who have significant mental health conditions,” Goldberg says. Many employers still have a limited understanding of workplace mental health issues.

When Dave approached his supervisor about accommodations, including a potential transfer to a position where he could have less direct contact with other employees, he was met with some hostility. He felt his boss brushed his concerns aside, and in May he left the organization. Now he has a new job as a peer specialist counseling people who are currently dealing with similar mental health issues. He has told his supervisors about his post-traumatic stress disorder. “I know they're not going to judge me, because they have been through their own story,” he says.