ADHD is a behavior disorder characterized by impairment in attention and/or hyperactivity that affects approximately 3-5% of children. Comorbid psychiatric illnesses including conduct disorders, depression and anxiety frequently occur with ADHD. Treatments include medications, behavioral treatments, and multimodal combinations of medication and behavioral treatments. The purpose of this study is to examine the threshold change in utility necessary between the symptomatic and well-controlled ADHD health states in order for each treatment to have an incremental cost-effectiveness ratio of less than $50,000-$100,000/QALY. Methods: We developed a model of ADHD health states, with and without psychiatric comorbidity, in order to assess the cost-effectiveness of treatments as defined by the NIMH Multimodal Treatments in ADHD (MTA) clinical trial. The MTA trial compared the treatments of managed medication and/or behavioral treatments to standard community care, and found that managed medication led to improvement in significantly more patients than community care, while adding behavioral treatments had a smaller benefit. Costs were estimated from the MTA clinical trial and published sources. The efficacy of treatments was taken from the MTA clinical trial. Results: Behavioral treatment alone is dominated. Managed medication, compared with community care, would need to produce a difference of .012 QALYs using base case assumptions for an incremental CE ratio of $50,000/QALY. Combined treatment of all patients would require a threshold difference of 0.94 QALYs between symptomatic and well-controlled ADHD. However, if only the patients with multiple comorbid illnesses are considered, the threshold difference for combined treatment is reduced to .495 for an incremental CE ratio of 50,000/ QALY, because multimodal treatment is most effective for this group. . Conclusions: The strategy of managed medication could produce an incremental cost-effectiveness ratio of less than $50,000/QALY with a very small improvement in QALYs. The addition of behavioral treatments to managed medication for all patients would require an additional improvement in QALYs that is so large it is unlikely to occur in clinical practice. However, in the subgroup of patients with multiple illnesses such as ADHD, depression and conduct disorder, an incremental cost-effectiveness ratio of less than $100,000 per QALY is possible for multimodal treatment, and the cost-effectiveness of adding behavioral treatment to managed medication merits further study.