This study examines the relation between neurologic, behavioral, and performance indicators of attention-deficit–hyperactivity disorder. Twenty-three males age nine to 11 years with attention-deficit–hyperactivity disorder, including symptoms of hyperactivity, and 23 matched controls served as participants. Differences between groups were investigated using referential 19-channel quantitative electroencephalogram, behavioral rating scale data, and continuous performance test data. Results from the behavioral data were consistent with previous research. Behavioral ratings for participants with attention-deficit–hyperactivity disorder were significantly more negative than controls. Control participants performed significantly better on the continuous performance test, with fewer errors, faster reaction times, and less variability in reaction time. Electroencephalogram results indicated differences between participants with attention-deficit–hyperactivity disorder and control participants primarily in the alpha bandpass, with evidence of increased alpha in posterior regions during baseline for the group with attention-deficit–hyperactivity disorder. Additionally, participants with attention-deficit–hyperactivity disorder manifested decreased alpha in left frontal regions when reading. The results are discussed in terms of possible differences in electroencephalographic data as a function of degree of hyperactivity, as well as the impact of task specificity on the electroencephalogram.