Objective: Attention deficit hyperactivity disorder (ADHD) is a costly public health problem. To the authors' knowledge, this is the first study on the cost-effectiveness of the major forms of ADHD treatments used in NIMH's Multimodal Treatment Study of Children With ADHD (MTA Study).Method: Five hundred seventy-nine children with ADHD, combined type, ages 7 to 9.9, were assigned to 14 months of medication management, behavioral treatment, both combined, or community care. Services were tallied throughout the study, including medication, health care visits, behavioral treatments, and rental costs. Provider specialty, total time, and number of visits with providers were used to calculate costs, adjusted to FY 2000 dollars with the consumer price index.Results: Treatment costs varied fourfold, with medication management being the least expensive, followed by behavioral treatment, and then combined treatment. Lower costs of medication treatment were found in the community care group, reflecting the less intensive (and less effective) nature of community-delivered treatment. Medical management was more effective but more costly than community care and more cost-effective than combination treatment and behavioral treatment alone. Under some conditions, combination treatment (medical management and psychotherapy) were somewhat more cost-effective, as demonstrated by lower costs per additional child "normalized" among children with multiple comorbid disorders.Conclusions: Medical management treatment, although not as effective as combined medical management and behavioral treatment, is likely to be more cost-effective in routine treatment for children with ADHD, particularly those without comorbid disorders. For some children with comorbid disorders, it may be cost-effective to provide combination treatment.