OBJECTIVES: This study was conducted naturalistically in order to observe the long-term effects of attention-deficit hyperactivity disorder (ADHD) medications on growth rates among Korean school-aged boys with ADHD. METHODS: Participants in the study were boys with ADHD aged 6 to 11 years who have taken ADHD medication, methylphenidate (extended release) or atomoxetine. They attended scheduled visits monthly or bimonthly for clinical assessment with measurement of height and weight. In this study, 35 boys with ADHD (mean age at baseline=7.90+/-1.77 years ; mean age at endpoint= 12.54+/-1.91 years) were included, with a mean follow-up period of 4.64 years (+/-1.62 years), ranging from 2 to 9.7 years. Height, weight, and body mass index (BMI) measurements were converted to "age-corrected Z-scores" using data from Growth Charts provided by the Korean Center for Disease Control and Prevention from 2007. RESULTS: Age-corrected endpoint growth parameters (height, weight, BMI Z-scores) did not differ significantly from the baseline values (height t=0.027 ; weight t=-0.61 ; BMI t=-1.86, in paired t-test). Especially high correlation was observed between the baseline and endpoint height Z-scores (r=0.876, p<.001), for which the coefficient of determination r2 was 0.767, meaning that the amount of variability in endpoint height Z-scores explained by the baseline height Z-scores was 76.7%. CONCLUSION: Our results suggested that the long-term effects of ADHD medications on growth parameters to be tolerable in Korean school-aged boys with ADHD.