Language impairments are commonly observed among children referred for psychiatric services. The most frequent psychiatric diagnosis of children with language impairment (LI) is Attention Deficit Hyperactivity Disorder (ADHD). It is not clear whether there are differences between children with ADHD and comorbid LI and children with other psychiatric disorders who are also comorbid for LI. In the present study the language, achievement, and cognitive processing characteristics of 166 psychiatrically referred 7–14-year-old children were examined using a 2 × 2 (ADHD, LI) design to examine four groups: children with ADHD+LI, children with ADHD who have normally developing language, children with psychiatric diagnoses other than ADHD with a language impairment (OPD+LI) or without a LI (OPD). Results indicated that children with LI were at the most disadvantage regardless of the nature of the psychiatric diagnosis. Contrary to prediction, working memory measures, used to tap the core cognitive deficit of ADHD in executive functions, were more closely associated with LI than with ADHD. It was concluded that caution must be exercised in attributing to children with ADHD what might be a reflection of problems for children with language impairment generally. As most therapies are verbally based it is notable that language competence is rarely evaluated systematically before such therapies are undertaken.