Background: In the treatment of adult ADHD the importance of psychological interventions in combination with pharmacotherapy is widely accepted in contemporary clinical routine. The natural course of the disorder seems to justify additional psychological interventions because even in patients who are highly compliant to pharmacotherapy full remission is not always achieved. In addition some of the specific impairments apart from comorbid disorders can be viewed as consequences of the chronic course of ADHD from early childhood into the adult life span. However empirical data on the efficacy of psychosocial interventions is still insufficient. Up to now there is only evidence that cognitive-behavioural approaches are efficient interventions, but there are few existing studies on psychosocial interventions in adult ADHD and some of them have substantial methodological flaws. Working Hypothesis: A combination of psychotherapy with pharmacotherapy shows an essential and incremental effect on ADHD symptom reduction in comparison to an exclusive pharmacological treatment with methylphenidate (MPH). Specific Aims: Apart from demonstrating the general efficacy of cognitivebehavioural therapy (CBT) on ADHD symptom reduction specific changes in different areas are expected to occur such as improvement in quality of life or in neuropsychological functioning. Methods: In a randomised controlled study, the efficacy of a combined treatment of psychotherapy with pharmacotherapy is compared to pharmacological intervention alone. After initiation and stabilisation of treatment with MPH in all subjects randomisation to the two different treatment conditions is done. After randomisation both groups will undergo treatment for about 10-12 weeks, the experimental group receiving 10-12 sessions of psychotherapy whereas the control group only receives medication and standard clinical management (SCM). Expected benefit: The study is expected to demonstrate the contribution of psychosocial interventions to pharmacological treatment of adult ADHD. If it can be proved that cognitive-behavioural interventions increase functioning and ameliorate quality of life, this will have an impact on everyday clinical practice and improved ADHD treatment. A manual for psychological interventions will facilitate transfer of skills to therapists such as physicians and psychologists. Considering economic and political aspects of health this therapy program may improve the quality of medical care for these patients and reduce the enormous costs that are caused by ADHD.