Adults with Attention Deficit Hyperactivity Disorder (ADHD) have impairments in attentional subsystems of alerting and conflict monitoring. Mindfulness meditation may lead to an improvement of these deficits, and reduces symptoms of anxiety and depression. However, the studies that demonstrated these improvements did not use a control group, nor controlled the use of medication. In the present study the investigators will examine the effects of the mindfulness practices (same protocol of 8 weekly sessions used in the study that showed positive effects in this disorder) in the performance of adult patients and healthy people (with ADHD). Cognitive performance, mood, and the quality of life will be assessed by validated questionnaires before and after treatment/standby.

Inclusion Criteria:

• Portuguese as their first language;
• minimum of eight years of formal education;
• normal vision or corrected to normal and normal hearing;
• no prior experience with meditation;
• patients should be taking stable doses of methylphenidate (for at least a month) for their disorder as prescribed by their doctors.

Exclusion Criteria:

• patients with neurological and psychiatric disorders such as psychosis, obsessive-compulsive disorder or Tourette's syndrome.