Psychopharmacological agents were shown to be important for improving the quality of life (QoL) of patients with attention-deficit/hyperactivity disorder (ADHD). A short-term, 10-week study found atomoxetine (ATX) to be effective in improving QoL of ADHD patients. We compared, for the first time, long-term treatment outcomes of ATX and other early standard therapy (OEST, any pharmacological ADHD treatment except ATX) in QoL and functional impairment in pharmacologically naive children/ adolescents in a randomized, controlled, open-label study at 6 and 12 months. Patients received ATX (0.5-1.8 mg/kg per day) or OEST (mainly methylphenidate). Quality of life and functioning were assessed by the Child Health and Illness Profile-Child Edition, Parent Rating Form and the Weiss Functional Impairment Rating Scale-Parent Report. Three hundred ninety-eight patients (79.4% male; mean age, 9.3 years) received study treatment. The Child Health and Illness Profile-Child Edition, Parent Rating Form achievement domain t scores significantly improved from baseline to 6 months from means of 28.0 to 37.1 for ATX and from 28.3 to 40.7 for OEST. Mean t scores at 12 months were 40.0 for ATX and 41.0 for OEST. The Weiss Functional Impairment Rating Scale-Parent Report total score improved from baseline to 6 months in both groups (ATX: mean 1.02 to 0.63; OEST: 0.96 to 0.59). Both treatments were safe with no statistically significant difference in the overall rate of adverse events. Overall, the improvements in QoL and functional impairment observed over time for ATX and OEST were meaningful and stable over the study period of 12 months. Between-group differences were small but sometimes statistically significant, providing the first-time long-term comparative symptomatic and QoL analysis between ATX and OEST.