Objective: This exploratory study measured the impact of comorbid anxiety disorders on sleep in children with ADHD and tested the effect of cognitive-behavioral therapy (CBT) on these measures. Method: Fifty-seven children (8-12 years old) were assessed with the Child Sleep Habits Questionnaire. Four groups were formed: ADHD (n = 20), ADHD + Anxiety (n = 20), Anxiety (n = 8), and Healthy Controls (n = 9). A subgroup of 10 children with ADHD + Anxiety underwent CBT for anxiety. Results: The results showed that sleep difficulties were better associated with anxiety than with ADHD. CBT reduced sleep onset latency and marginally decreased the total amount of sleep problems. Conclusion: The present study demonstrates that comorbid anxiety in ADHD children is linked with specific sleep disturbances and is sensitive to CBT aimed at reducing anxiety.