The current study explored the relationship between middle frontal gyrus (MFG) volume and working memory in children with Attention-Deficit/Hyperactivity Disorder (ADHD) and dyslexia (RD). it was hypothesized that there would be group differences in middle frontal gyrus volume and working memory performance, and that there would be a relationship between middle frontal gyrus volume and working memory performance. Results indicated that there was a trend of smaller left hemisphere middle frontal gyrus volumes in the RD groups compared to the non-RD groups. In addition, when total brain volume, Passage Comprehension and Attention Problems were included as covariates, Sequences, a verbal working memory task, significantly predicted left MFG volume. Finally, when exploratory analyses were conducted, Passage Comprehension significantly predicted both left and right MFG volumes when both Reading Fluency and Letter Word Identification were also included in the model as predictors. Little research has been conducted on the relationship between MFG volumes and RD and ADHD groups. Significant findings and trends reported here related to RD groups and reading-related tasks indicate that further research exploring the relationship between complex working memory tasks like Passage Comprehension and MFG volumes is warranted.