The available literature provides few studies on the effectiveness of methylphenidate in improving quality of life in individuals with ADHD. Objective: To assess the effectiveness of Methyphenidate OROS formulation (OROS MPH) through QoL in adults with ADHD. Method: A 12-week, multicenter, open-label trial involving 60 patients was used. The measures used were Adult Self-Rating Scale, Adult ADHD Quality of Life Scale (AAQoL), State and Trait Anxiety Inventory (STAI), Hamilton Depression Rating Scale (HAM-D), Clinical Global Impression (CGI), and safety measures. A significance statistic level of 5% was adopted. Results: Analyses included 60 patients (66.7% male; M age = 31.1 years) for safety and 58 patients for effectiveness. All AAQoL subscales improved from baseline to Week 12 (p less than .0001), as well as the Total AAQoL (p less than .0001). A significant reduction on Clinical Global Impression--Improvement (CGI-I), HAM-D, STAI, and ASRS scores was observed (p less than .0001). No serious adverse event was reported. Conclusion: Treatment of adult ADHD patients with OROS MPH improves QoL. (Contains 5 figures.)