The present study examined whether deficits in inhibitory control in preschool-aged children are predictive of attention-deficit/hyperactivity disorder (ADHD) symptoms and certain social difficulties in middle childhood, specifically third grade. Although many studies have examined the concurrent relationships among disinhibition, ADHD and social competence, few have focused on the preschool-aged population and the longitudinal relationship between early inhibition and later ADHD symptoms and social skills. Using a non-referred sample of children, laboratory measures of inhibition administered at 54 months of age, and parent/primary caregiver and teacher ratings of ADHD behaviors and social skills at third grade, the study revealed a significant but modest relationship between early disinhibition and later ADHD symptoms and social difficulties. Regression analysis indicated that early difficulties with inhibitory control could explain little of the variance in later inattention, hyperactivity/impulsivity and social competence. (Contains 4 tables.)