Purpose: Attention-deficit/hyperactivity disorder (ADHD) is a multifactorial disorder that has been linked to increased risk for behavioral, academic, and interpersonal problems. Developmental language disorder (DLD) has also been linked to poor outcomes in these areas. The presence of co-occurring disorders in children's profiles is generally associated with poorer outcomes relative to profiles consisting of only one disorder. This study investigated the extent to which co-occurring DLD in children already identified with ADHD presented increased risk for severity of their primary ADHD symptoms, the presence of secondary behavioral problems, and/or increased problems in the tertiary areas of academic performance and interpersonal interactions. Method: Data from 90 children from combined community-based and clinically based study samples were used in this retrospective study. Behavioral, academic, and social attributes were assessed from parent ratings on the Child Behavior Checklist. Results: Results indicated primary symptoms of ADHD and related tertiary interpersonal consequences were not increased when co-occurring DLD was present. However, the co-occurrence of DLD on ADHD resulted in increased risk for secondary externalizing problems and deficits in academic performance. Conclusions: Outcomes highlight the need for high-quality collaborations among clinical professionals, school-based professionals, and parents to ensure the complex needs of children with ADHD are adequately addressed. Children with ADHD who have elevated externalizing behaviors and who are struggling academically should be tested for possible co-occurring DLD.