Attention-Deficit/Hyperactivity Disorder (AD/HD) is the most common psychiatric disorder of childhood, but it is becoming increasingly apparent that more than half the childhood sufferers will continue to manifest symptoms of the disorder as adults. While the EEG of children with AD/HD has been extensively examined, comparatively little research has been conducted into the EEG of adults with the disorder. This study thus investigated the EEG of 20 adult males with AD/HD, and an age- and gender-matched control group, during an eyes-closed resting condition. The EEG was Fourier transformed to provide absolute and relative power estimates for the delta, theta, alpha and beta bands. The AD/HD group had significantly less absolute delta and more relative theta, across the entire scalp, than the control group. In absolute beta, the AD/HD group had less power at the midline, and an enhancement in power in the right posterior region. These results are similar to those found in children with AD/HD, and may suggest the presence of a processing deficit. A right posterior elevation in beta activity was also found, which could be related to the ongoing presence of reading disabilities in these subjects.