Attention-deficit hyperactivity disorder (ADHD) is the most common psychiatric disorder in children and adolescents. Symptoms of ADHD and its treatment can impact an individual's quality of life (QoL). The present study aimed to evaluate the effect of atomoxetine treatment, demographic characteristics, and seasonal variation on QoL in children with a recent diagnosis of ADHD and their parents. The present study included a cohort of 200 children diagnosed with ADHD. In addition to the recruited children, one of their parents was included in the study. ADHD symptoms were assessed using Conners' Parent Rating Scale. QoL of the participants was assessed with the PedsQL, while parents' QoL was evaluated using the World Health Organization Quality of Life questionnaire (WHOQOL-Bref). There was significant improvement in pediatric and parental QoL after treatment with atomoxetine. Significant factors related to better QoL in the participants included spring season, above average Conner's score, male sex, and rural residence. However, after using multivariate regression analysis, only patients' sex and Conner's score were significant predictors of pediatric QoL at the end of treatment with atomoxetine. Medical treatment significantly improved QoL in children with ADHD and their parents. Level of improvement was affected by patients' sex and ADHD severity.