Attention-deficit hyperactivity disorder (ADHD) is a condition distinct from bipolar disorder, but the differentiation of mania from ADHD can be difficult.  There are similarities in symptoms, particularly in the differential diagnosis of children and adolescents.  It has been argued that ADHD is misdiagnosed in some young people who actually have bipolar disorder, although a high number of youth with bipolar disorder also have ADHD.  The coexistence of the two conditions may be related to the age of onset of bipolar disorder, as adults with a reported history of comorbid ADHD tend to have the onset of bipolar disorder before age 19.  Studies of rates of ADHD in the children of bipolar adults have found higher rates than in control subjects.

Both disorders share many characteristics such as impulsivity, inattention, hyperactivity, high physical energy, mood swings, frequent coexistence of conduct disorder and oppositional-defiant disorder, and learning problems.  Family history in both conditions often has the presence of mood disorders.  Elevated mood and grandiosity are the symptoms best able to distinquish between pediatric bipolar disorder and ADHD.  Also, with bipolar disorder, hyperactivity may be more episodic.  Irritability, hyperactivity, accelerated speech, and distractibilty are frequent in both childhood-onset bipolar disorder and ADHD and are not useful in differentiating between the two disorders.  The response or lack of response to stimulant medications is not diagnostically helpful, but classification of the diagnosis is important as stimulants can promote mania in a bipolar individual if not on a mood stabilizer first (as with antidepressants).