Of a consecutive series of 115 boys diagnosed in a university outpatient clinic as ADHD, 39% also demonstrated a specific reading disability. Pure ADHD patients were compared with mixed ADHD + RD and normal controls on a battery of cognitive and attentional measures. The aim was to determine whether a distinct pattern of deficits would distinguish the groups. Both ADHD subgroups performed significantly worse than controls on measures of sequential memory and attentional tasks involving impulse control and planful organization. Only ADHD + RD boys differed from controls on measures or rapid word naming and vocabulary. The results are discussed within the framework of an automatic versus effortful information-processing model.