Attempted to clarify the nature of the sustained and selective attention deficits implicated in attention deficit hyperactivity disorder (ADHD). Specifically, performance on the Continuous Performance Test (CPT, Sergeant & van der Meere, 1990) and speeded classification task was assessed for a group of 7- to 12-year-old ADHD boys and their same-aged normal peers. Results of the CPT indicated that both perceptual sensitivity and omission errors increased over time for the ADHD boys to a greater degree than for the control boys, findings indicative of a sustained attention deficit. Results of the speeded classification task indicated that ADHD children's performance was not as efficient as normal children. However, there was no evidence for a selective attention deficit. Findings are discussed in terms of a process-energy model of attention.