http://bipolarchild.com/newsletters/0611.html
A Closer Look at Problematic Boundary Issues: ADHD and Bipolar Disorder

At least seven of the DSM-IV criteria used to diagnose ADHD are commonly shared with bipolar disorder as it presents in childhood. A study of 1200 cases diagnosed with pediatric bipolar disorder performed by researchers of the Juvenile Bipolar Research Foundation found exceedingly high rates of endorsement of these "ADHD" symptoms:

Easily distracted by extraneous stimuli 96%
Difficulty sustaining attention in tasks or play 96%
Restlessness as if driven by a motor 71%
Often talks excessively 80%
Difficulty waiting turn 96%
Blurts thoughts out 96%
Often has difficulty organizing tasks 91%
Many of the most commonly used diagnostic inventories employed by mental health professionals to diagnose ADHD include symptoms that would be indistinguishable from the most common symptomatic profiles observed in children with bipolar disorder. Therefore, since attentional problems, motor disinhibition, and organizational deficits are part and parcel of both conditions, it is difficult to make a clear diagnosis.

If a clinician diagnoses according to strict DSM-IV criteria, and there are symptoms of mania present also, than, as we mentioned earlier, both bipolar disorder and ADHD must be diagnosed as co-occurring disorders