ADHD is associated with spatial working memory deficits, thought to be subserved by dysfunction of neural circuits. In this study we aimed to further examine fronto-parietal dysfunction in ADHD by examining brain activation associated with the Raven’s Progressive Matrices task, a visuo-spatial pattern sequencing task involving relational reasoning and thereby placing high-demand loading on the prefrontal cortex. Functional MRI was conducted on twelve right-handed 8–12 year old boys with ADHD-combined type and 12 right-handed, age and performance IQ-matched, healthy boys as they completed items from the Raven’s Progressive Matrices. Our findings further confirm striatum and parietal lobe dysfunction in ADHD. Furthermore, dysfunction in lateral prefrontal regions was found. In addition to lateral prefrontal, striatum and posterior parietal regions, the temporal lobe was also less active. These findings suggest deficits in a widespread ‘functional network’ in ADHD that may be fundamental for visuo-spatial information processing and relational reasoning.