The effects of 0.3 mg/kg methylphenidate were compared for 12 ADD boys and 12 ADD girls participating in a summer treatment program for children with behavior and/or learning problems. Previous investigations have suggested that ADD girls may differ from ADD boys in some important respects. No information exists regarding whether the effects of the most common treatment for these children, methylphenidate, has comparable effects on boys and girls. The boys and girls were matched for age and IQ. The results revealed equivalent and beneficial effects of methylphenidate for both boys and girls. Methylphenidate therefore would appear to be as useful a treatment for ADD girls as for ADD boys.