OBJECTIVES: Parents of children with attention deficit hyperactivity disorder (ADHD) report problems with the need to take medication three times per day. These problems include storage and administration of a controlled substance at school and the stigmatising impact on the child. The present study was designed to estimate the utility gain associated with switching to a once per day sustained release (OROS) treatment. METHODS: Clinical data from OROS methylphenidate trials were used to define health states associated with monotherapy and combination therapy (addition of behavioural therapy). To determine the utility gain with once daily therapy, the monotherapy and combination therapy health states were further distinguished to specify frequency of dosing. Forty two interviews with parents of children with ADHD were conducted where parents were asked to rate the health states using a visual analogue scale (VAS) and standard gamble (SG). RESULTS: The 1 per-day treatment was given a higher valuation with the VAS ratings being 66.3 (±6.6) for the sustained release formulation and 51.0 (±7.2) for the immediate release formulation. A difference was also observed in the SG ratings with 0.90 (±0.05) and 0.86 (±0.07) for the sustained release formulation and immediate release formulation, respectively. These results were confirmed by the valuations of the combination therapy health states. In general, the ratings for monotherapy were given a higher valuation than combination therapy. CONCLUSIONS: In this study, the health states assumed equal effectiveness between a once-daily and a three times daily preparation, in order to assess the utility difference resulting only from frequency of dosing. Participants showed a preference for ADHD treatments with once daily dosing.