OBJECTIVES: The discussion on compliance versus non-compliance exercises many minds in ADHD. Given the potential economic impact, we investigated societal costs among compliant and non-compliant children with ADHD. METHODS: A cross-sectional retrospective survey among parents of a child aged 6-18 (members of the Dutch patient organization) with ADHD was conducted in September 2010. The TiC-P questionnaire was used to collect data on medical and non-medical resource use. Reference prices (2010) from the Netherlands were taken as unit costs. Differences were analysed using Students’ t-tests. Compliance status was based on parent evaluation and based on pre-defined definitions supported by expert opinion. RESULTS: This first analysis was based on 473 and 219 children who were compliant or non-compliant to pharmacological treatment, respectively. Mean age was 11.2 years, 82.8% were boys. Compliance had a significant influence on total treatment costs, with total mean monthly costs being €543 (SD € 1141) and €879 (SD €1368) for compliant and non-compliant children, respectively (p=0.001). The most important cost items were medical consultations (23.4% vs. 26.3%), coaching and extra support lessons at school (24.0% vs. 18.5%), skills trainings (18.2% vs. 19.0%), and child day care (13.8% vs. 11.0%). Medication constituted 4.8% and  2.7% of total costs. Next to compliance, regression analysis showed that comorbidity also had a significant influence on total treatment costs (p=0.000). In a regression model in which compliance and comorbidity were independent variables, both were significant (p=0.003 and p=0.000, respectively). Mean costs were €253 and €659 (compliant vs. non-compliant) for children without comorbidity and €669 and €950 for children with comorbidity. Adding a dummy for comorbidity*compliance did not show a significant interaction between the two. CONCLUSIONS: Children compliant to ADHD medication have significant lower monthly costs compared to non-compliant children. So, effective methods to improve compliance medication in this patient population may be cost-effective.