The symptoms experienced by people with mild closed-head injury (mCHI) and by people with attention deficit disorder (ADD) are similar in many aspects. We examined the performance of 26 adults with mCHI, 23 adults with ADD, and 25 matched controls on four functional areas: (1) simple motor response, (2) response speed and attention, (3) complex perceptual-motor performance, and (4) memory and learning. Analyses of variance and multivariate analyses of variance were used to compare the performance of the three groups. Test results were also plotted to examine patterns of performance and similarities between the groups. Both groups with mCHI and ADD had significantly more difficulty than controls with sustained attention. However, whereas the group with mCHI was characterized by generalized slowness in their response times, the group with ADD was characterized by impulsivity or an inability to regulate their attention and responses.