The first objective is to measure the QALYs (Quality Adjusted Life Years) of Brazilian children and adolescents, submitted to methylphenidate immediate-release treatment for Attention Deficit Hyperactivity Disorder (ADHD). For this, the Health Utility Index scale (HUI) will be completed by the patient and/or family, in two moments of an observation study with immediate-release methylphenidate: at the baseline and 6th month of treatment in the follow-up. The results provides information to calculate the utility measure and determine the QALYs (Quality Adjusted Life Years). After this, for the cost-effectiveness of the treatment, it will be used a Markov model of decision analysis, and a Monte Carlo simulation with 10,000 random trials.