Objective: Emotional impulsiveness (EI) may be a central feature of attention-deficit/hyperactivity disorder (ADHD) contributing impairment beyond the two ADHD dimensions of inattention and hyperactivity-impulsivity. Method: We evaluated EI in hyperactive (N = 135) and control (N = 75) children followed to adulthood (mean age 27 years). The hyperactive cases were subdivided into those individuals whose ADHD persisted (ADHD-P) and did not persist (ADHD-NP) to adulthood. We examined the additional contribution of EI apart from ADHD symptoms to global ratings of impairment in 10 major life activities, adverse occupational and educational outcomes, criminal and driving outcomes, and money management difficulties at ages 21 and 27. Results: The ADHD-P group reported more EI symptoms than either the ADHD-NP or community control groups. EI uniquely contributed to seven of 10 major life domains and to overall impairment beyond ADHD symptoms. Severity of EI uniquely contributed to numerous impairments in occupational, educational, criminal, driving, and financial outcomes beyond ADHD symptoms. Conclusions: EI is as much a component of ADHD as are its two traditional dimensions and is associated with impairments beyond those contributed by the two traditional dimensions. (Contains 1 figure and 4 tables.)