OBJECTIVE: To evaluate the number of patients reaching stable treatment with a stimulant (methylphenidate or dexamphetamine) or non-stimulant (atomoxetine) attention-deficit/hyperactivity disorder (ADHD) medication approved for use in the Netherlans, and the time to treatment stabilization among children and adolescents aged 6-17 years. RESEARCH DESIGN AND METHODS: Prescription data from the PHARMO medical record linkage system from 48 geo-demographic areas in the Netherlands (2003-2006) were analyzed from newly treated patients with ADHD aged 6-17 years. Only patients with >/= 5 dispensings for any ADHD drug during follow-up (at least 12 months) and no missing information on type of drug, strength, and number of pills per day were included. MAINOUTCOME MEASURES: Attainment of a stable dosing regimen was defined as no change in type of drug (including a switch from an immediate release (IR) to a long-acting (LA) formulation), strength, and number of pills per day for five consecutive dispensings. Time to stable dosing regimen was defined as the number of days between the first dispensing for an ADHD drug and the first of five unchanged dispensings. RESULTS: Of 4909 children or adolescents initiating treatment, 3099 met selection criteria. Morepatients starting therapy with LA methylphenidate (82.4%) achieved treatment stabilization during follow-up than with IR methylphenidate (74.8%; p < 0.01) or atomoxetine (69.8%; p < 0.05). More patients initiated on LA methylphenidate patients (43.9%) achieved treatment stabilization without changing their index medication or dose compared to those initiated on IR methylphenidate (25.3%) or atomoxetine (8.1%; p < 0.0001 for both comparisons). Among patients achieving treatment stabilization, those initiating treatment with LA methylphenidate had a significantly shorter time to treatment stabilization (14 days) than patients initially treated with IR methylphenidate (56 days; p < 0.001) or atomoxetine (31 days; p < 0.05). Mean number of pills per day varied between 1.0 and 1.8 at initial treatment and 1.1 and 1.9 at treatment stabilization. Potential limitations of the study include the use of ADHD-medication dispensing as a proxy for an ADHD diagnosis and the impact of different titration schedules for the various ADHD medications. CONCLUSION: Overall, 2316 of the 3066 eligible patients (75.5%) achieved treatment stabilization during follow-up. Among children and adolescents with ADHD in the Netherlands, the time to treatment stabilization varied according to choice of initial treatment and was shortest for LA methylphenidate.