National Alliance for the Mentally Ill (NAMI) is a national advocacy organization for those affected by mental illness in our country. NAMI provides general information and support opportunities for many mental illnesses. This link provides a fact sheet for ADHD.
National Institute of Mental Health held a consensus conference on Attention-Deficit/Hyperactivity Disorder in November, 1998. Searching this site, you will find the consensus statement that came from the meeting.