The growth in height and weight of 86 hyperactive children receiving methylphenidate hydrochloride (average, 40 mg/day for up to four years) was compared with general population norms on recently updated growth charts. A significant decrease in height percentile was apparent after 2, 3, and 4 years of treatment but not after one year. A significant loss in weight percentile occurred onward from the first year of treatment. Dosage was significantly associated with the decrease in height and weight percentile. Greater initial height and weight were associated with greater growth decrements. The use of adjunctive thioridazine hydrochloride (mean, 87 mg/day) did not influence the growth of children receiving methylphenidate. Although the magnitude of the growth suppressant effect in groups was small (dosage accounted for only 2% of the variance in final height), the results suggest that clinicians should monitor the growth of hyperactive children receiving stimulants and consider dosage reduction in individual cases should evidence of growth suppression occur.