Attention-Deficit/Hyperactivity Disorder (AD/HD) is the most common psychiatric disorder of childhood, but it is becoming increasingly more apparent that more than half the childhood sufferers will continue to manifest symptoms of the disorder as adults. While EEG coherence in children with AD/HD has been examined extensively, no studies have investigated coherence in adults with the disorder. This study investigated EEG coherence in adults with AD/HD. EEG was recorded from 18 adult males with AD/HD, and an age- and gender-matched control group, during an eyes-closed resting condition. Waveshape coherence was calculated for 8 intrahemispheric electrode pairs (4 in each hemisphere), and 8 interhemispheric electrode pairs, within each of the delta, theta, alpha and beta bands. A laterality effect was found for intrahemispheric coherence at long inter-electrode distances, with the AD/HD group showing reduced hemispheric differences in the delta band compared to the control group. In the alpha band, at short-medium inter-electrode distances, the AD/HD group also had lower coherences than the control group. The results suggest that theta coherence differences reported in children with AD/HD may be associated with hyperactivity, which is reduced in adults with AD/HD, while reduced alpha coherence could be associated with inattention, which remains in adult with AD/HD. Reduced delta coherence also appears to be an aspect of the disorder which may develop from later childhood into adolescence and adulthood.