Purpose: Few studies have assessed listening effort (LE)--the cognitive resources required to perceive speech--among populations with intact hearing but reduced availability of cognitive resources. Attention/deficit/hyperactivity disorder (ADHD) is theorized to restrict attention span, possibly making speech perception in adverse conditions more challenging. This study examined the effect of ADHD on LE among adults using a behavioral dual-task paradigm (DTP). Method: Thirty-nine normal-hearing adults (aged 21-27 years) participated: 19 with ADHD (ADHD group) and 20 without ADHD (control group). Baseline group differences were measured in visual and auditory attention as well as speech perception. LE using DTP was assessed as the performance difference on a visual-motor task versus a simultaneous auditory and visual-motor task. Results: Group differences in attention were confirmed by differences in visual attention (larger reaction times between congruent and incongruent conditions) and auditory attention (lower accuracy in the presence of distractors) among the ADHD group, compared to the controls. LE was greater among the ADHD group than the control group. Nevertheless, no group differences were found in speech perception. Conclusions: LE is increased among those with ADHD. As a DTP assumes limited cognitive capacity to allocate attentional resources, LE among those with ADHD may be increased because higher level cognitive processes are more taxed in this population. Studies on LE using a DTP should take into consideration mechanisms of selective and divided attention. Among young adults who need to continuously process great volumes of auditory and visual information, much more effort may be expended by those with ADHD than those without it. As a result, those with ADHD may be more prone to fatigue and irritability, similar to those who are engaged in more outwardly demanding tasks.