This paper reports early findings from a wider study that sought to test the hypothesis that differences in language use exist between children who have a diagnosis of Attention Deficit Hyperactivity Disorder (ADHD) and their non-ADHD peers. Twenty-two, 8 to 12 year-old children (11 with a diagnosis of ADHD and 11 matched peers) comprised the community-based sample. There were nine boys and two girls in each group. All the children were ranked at least average for their language ability on standardised language testing. This case-control study used an approach derived from Systemic Functional Linguistics (SFL) to examine and then compare spoken and written elicited language samples. SFL was thought to be particularly suitable because of its potential to richly describe language in use while taking contextual variation into account. Statistically significant overall differences between the subject and the control groups were found for the measure of grammatical intricacy (GI). Further analyses revealed these differences to be largely attributed to differences between group scores for written material. Discussion explores the potential relevance of these findings to the clinical evaluation of language ability in young school-aged children who have been diagnosed with ADHD.