Attention deficit/hyperactivity disorder (ADHD) can sometimes coexist with bipolar disorder (BD). Despite controversies about the coexistence of the two disorders, recent clinical as well as biological studies support the concept of comorbid adult ADHD and BD. Although there is some overlapping symptomatology between both disorders, ADHD can be diagnosed in patients suffering from with BD after a detailed clinical evaluation. Clinicians should be particularly attentive to specific symptoms in order to treat adequately both disorders since untreated ADHD comorbidity with BD is associated with poor clinical and socio-professional outcome.