This cross-sectional case-control study compared sleep problems in consecutively referred children aged 7-13 years meeting DSM-IV criteria for anxiety disorder, attention deficit/hyperactivity disorder (ADHD), comorbid anxiety disorder and ADHD, and a group of control children of similar age and gender. Diagnoses were assessed with the Kiddie-SADS PL interview, parent form, and the sleep problems with a standardized sleep questionnaire, the Children's Sleep Habits Questionnaire (CSHQ), as reported by the mother. A total of 141 children were included (anxiety disorder (n = 41), ADHD (n = 39), comorbid condition (n = 25), controls (n = 36)). Children in the clinical groups had more sleep problems than controls. Children with anxiety disorders and children with comorbid condition were reported to have more sleep problems than children with ADHD alone. Night waking was associated with comorbid anxiety disorder and ADHD. Bedtime resistance was associated with anxiety disorder, while daytime sleepiness affected all clinical groups. Clinical management of children with ADHD and anxiety disorders needs to include assessment of sleep problems.