OBJECTIVES: To evaluate time to optimization of dose in children with ADHD in the Netherlands. METHODS: Claims data from the PHARMO medical record linkage system database from 48 geo-demographic areas in the Netherlands (2003–2006) were analyzed from newly treated ADHD patients aged 6–17 years. Patients were followed for at least 12 months after treatment initiation with methylphenidate or atomoxetine. Demographic and medication characteristics at treatment initiation, and concurrent psychotropic treatments in the year before ADHD treatment initiation were recorded. For this analysis, only patients with ³5 dispensings for any ADHD drug during follow-up and no missing information on type of drug, strength, and number of pills per day were included. Optimized dosing regimen was defined as no change in type of drug, strength, and number of pills per day for 5 consecutive dispensings (no time restriction between dispensings). Time to optimized dosing regimen was defined as the number of days between the first dispensing for an ADHD drug (cohort entry date) and the first of five unchanged dispensings.   RESULTS: Of 4909 children initiating treatment from 2003–2006, 3159 met selection criteria. The proportion of patients reaching dosing optimization with initial treatment was 69.8% for atomoxetine (ATX; n=37), 74.8% for short-acting methylphenidate (SA; n=2017), and 82.4% for long-acting methylphenidate (LA; n=262; P<0.05 for both ATX and SA vs LA). The median number of days required to reach optimal dosing regimen was 49 across the total sample. Among patients achieving dose optimization, those initiating treatment with LA had a significantly shorter time to dose optimization (14 days) than patients initially treated with SA (56 days; P<0.001) or ATX (31 days; P<0.05). CONCLUSIONS: Time to optimization of dosing regimen in children with ADHD in the Netherlands varied according to treatment chosen at initiation and was shortest for long-acting methylphenidate. Supported by funding from Shire Development Inc.