OBJECTIVES: To model the treatment patterns of ADHD and to assess health economic differences between standard immediate-release methylphenidate (MPH-IR) (OD, BID or TID); a new orally administered, once-daily (OD), long-acting (LA) formulation of methylphenidate using a unique osmotic release delivery technology (MPH-OD, LA); and behavioural therapy (BEH) in the UK. The use of MPH-OD, LA minimizes fluctuations in peak-trough concentrations improving acute tolerance. METHODS: Based on a clinical trial by the MTA Cooperative Group, a medical decision tree was developed in MS-Excel, reflecting the current treatment strategies and associated outcomes. The profile for MPH-OD, LA was determined based on a short-term comparative double-blind cross-over trial and a 24-month open-label multicenter study. The adjusted expected treatment success was 78.4% for MPH-OD, LA compared to 55.6% for MPH-IR and 33.8 % for BEH. Treatment switches or combinations due to adverse events or inefficacy, and a more intensive follow-up for patients with comorbidities were accounted for. To identify the resource use associated with each treatment, 6 centres were asked to provide data on their management of ADHD in patients between 6 and 16 years old. Data on interventions from parents/caregivers and teachers were additionally gathered. The analytical time horizon was one year. RESULTS: Treatment switches to behavioural treatment occur in 11.8% of MPH-OD, LA and 24.2% of MPH-IR patients. Starting treatment with BEH alone resulted in the highest annual cost (3,453 Euro), while starting treatment with MPH-IR alone (2,138 Euro) and MPH-OD, LA alone (2,187 Euro) generated a comparable cost. Probabilistic sensitivity analyses showed that the results were sensitive towards treatment success and the proportion of patients with comorbidities. CONCLUSIONS: UK treatment costs over one year appear comparable regardless of whether patients were treated first with MPH-OD, LA or MPH-IR. Treating patients first with BEH and then adding stimulant medication if needed resulted in higher overall annual treatment costs.