Duplication of chromosome 15q11.2-q13.1 (dup15q syndrome) results in hypotonia, intellectual disability (ID), and autism symptomatology. Clinical electroencephalography has shown abnormal sleep physiology, but no studies have characterized sleep behaviors. The present study used the Children's Sleep Habits Questionnaire (CSHQ) in 42 people with dup15q syndrome to examine the clinical utility of this questionnaire and quantify behavioral sleep patterns in dup15q syndrome. Individuals with fully completed forms (56%) had higher cognitive abilities than those with partially completed forms. Overall, caregivers indicated a high rate of sleep disturbance, though ratings differed by epilepsy status. Results suggest that clinicians should use caution when using standardized questionnaires and consider epilepsy status when screening for sleep problems in dup15q syndrome.