OBJECTIVES: To characterize patient sample, treatment patterns, and provide 1-year costs of an ongoing observational study of pediatric Attention Deficit/Hyperactivity Disorder (ADHD) patients in Europe. METHODS: AUTOR is a European observational study investigating factors associated with ADHD severity changes across a 2-year follow-up period in patients aged 6-17 that are stable responders on their first pharmacotherapy. At baseline, patients must have taken their ADHD medication for 3-8 months and have a Clinical Global Impression Severity score ≤3 and Improvement score ≤2 compared to treatment initiation. Data were collected at months 0, 3, 6, 9, 12, 18, and 24. UK unit costs of health & social care (PSSRU 2011) were used for analysis. RESULTS: A total of 703 patients (Italy: 224 [32%], Romania: 196 [28%], Greece: 125 [18%], UK: 72 [10%], Slovenia: 42 [6%], Sweden: 21 [3%], Netherlands: 17 [2.4%], Denmark: 6 [1%]) were analyzed (98 out of 801 failed to meet entry criteria). Patient characteristics: mean (SD) age 10.7 (2.7) years, 99% Caucasian, 82% male, 76% combined ADHD subtype. Most prominent baseline comorbidities: oppositional defiant disorder (28%), anxiety (15%), dyslexia (20%), and other learning disorders (33%). Baseline medication: Stimulants=298 patients (51% methylphenidate, 49% long-acting methylphenidate), atomoxetine=393 patients, other pharmacotherapy=8 patients, drug combination=4 patients. Mean (SD) treatment duration before baseline: 4.9 (1.5) months. Mean (SD) total costs after 1 year: £7520 (7374.5), split into £3618 (4171.7) direct costs excluding treatment (48%), £1783 (2933.6) treatment costs (24%), and £2119 (4911.2) indirect costs (28%). After 1 year, 82 patients (12%) have discontinued and 621 patients (88%) are ongoing. CONCLUSIONS: The AUTOR sample differs from clinical trials in its higher prevalence of comorbid conditions. There is substantial 1-year mean cost associated with pediatric ADHD, even for stable responders on their pharmacotherapy. Notably, only one quarter of the cost of ADHD is due to medication.