ADHD and bipolar disorder co-occur frequently in children but is less recognized in adults. This presentation will review the data on the co-occurrence of these two disorders in adults, the prevalence as well as clinical implications for severity and course of bipolar disorder. While the prevalence in clinical populations will over-estimate how often they co-occur (Berkson’s Bias), those data have profound implications for clinicians. Furthermore, its important to tease apart the cognitive impairments associated with bipolar disorder (during acute episodes as well as between episodes) from what is specific to co-occurring ADHD. Finally, I will review the small amount of available data on the treatment of ADHD comorbid with bipolar disorder and the benefits and risks of stimulants in this population.