Objective: To investigate whether prolonged therapy with a long-acting stimulant affects growth in children with attention-deficit/hyperactivity disorder (ADHD). Method: One hundred seventy-eight children ages 6 to 13 years received OROS methylphenidate (OROS MPH, CONCERTA) for at least 21 months. Height and weight were measured monthly during the first year and every 3 months thereafter. Results: At baseline, subjects were approximately the expected height for their age and somewhat heavier than expected. Subjects gained height steadily throughout the study and were on average 0.23 cm less than expected at month 21. Weight did not increase and BMI decreased slightly in the first 4 months. Thereafter, weight Z score and BMI Z score remained relatively constant and children were on average 1.23 kg less than expected at month 21. Previous stimulant therapy tended to be associated with a smaller decrease in Z score during the study compared with no previous stimulant therapy. Drug holidays did not significantly affect growth. Conclusions: The effects of prolonged OROS MPH therapy on growth were clinically insignificant and limited to slight decreases in weight during the first months of therapy. Drug holidays did not reduce any impact on growth and are thus of questionable utility for limiting potential effects of treatment on growth. (Contains 3 figures and 3 tables.)