Objective: To further define the nature of working memory (WM) impairments in children with combined-type ADHD. Method: A total of 40 Children with ADHD and an age and gender-matched control group (n = 40) completed two measures of visuo-spatial WM and two measures of verbal WM. The effects of age and learning/language difficulties on performance were evaluated. Results: Children with ADHD obtained significantly lower scores than controls on measures of both visuo-spatial and verbal WM. The impairments in verbal WM were age related. Conclusion: Children with ADHD exhibit impaired visuo-spatial WM performance. Younger (less than 8 years), but not older, children with ADHD demonstrate impairments in verbal WM. This latter result may explain the previously reported inconsistent performance of children with ADHD on verbal WM tasks. The importance of taking a developmental perspective in WM research is stressed. (Contains 4 tables.)