The article focuses on Attention Deficit/Hyperactivity Disorder (ADHD), which affects a substantial proportion of the adult population and it often remains undiagnosed. Because of its symptoms, which include inability to focus and maintain attention, problems in time management and procrastination, ADHD is suspected as a cause of poor performance in the workplace. A recent contemplation suggests a mechanism for that: employees with ADHD may perform less well because they are unable to focus their attention at tasks that have a long-term consequence for job accomplishment, but they instead pay attention at tasks that require immediate attention, such as responding to a low priority e-mail, but are of less long-term importance for the job. In essence, this means that employees with ADHD may still demonstrate strong effort, but they are unable to translate that effort into actual work performance because they focus on low value-adding tasks. A series of studies have provided substantial support for that reasoning. The studies not only confirmed that ADHD is associated with reduced job performance, but they also demonstrated that ADHD does not allow employee effort to translate into performance on the job. What the findings also implied is that those with ADHD are probably unaware that their effort does not translate into performance, so they keep working inefficiently, albeit hard. The findings make important implications for practice and how to deal with ADHD in the workplace, given that ADHD may be affecting one in ten workers.