Previous studies suggest that individuals with Williams syndrome (WS), a rare genetically based neurodevelopmental disorder, show specific weaknesses in visual attention and response inhibition within the visuospatial domain. Here we examine the extent to which impairments in attentional control extend to the visuomotor domain using a well-validated measure of choice stepping reaction time (CSRT) in individuals with WS. We examined the interaction between executive control and visually guided stepping using a verbal fluency dual-task or Go/NoGo paradigm during CSRT performance. Relationships between dual-task and inhibitory stepping and behavioural inattention and hyperactivity were also examined. Our results showed clear dual-task costs in stepping response times when performing a concurrent cognitive task in the WS group when compared to spatial and verbal ability matched typically developing controls. Although no group differences in stepping accuracy were observed between the WS and typically developing control groups, the WS group showed progressive slowing and more variable response times across the duration of the Go/NoGo task. These results suggest dysfunction in circuits involved in top-down attentional control processes in WS. These findings provide novel evidence that core executive control deficits in WS extend to the visuomotor domain, and impact on ADHD-related inattentive symptoms.