Mowat–Wilson syndrome (MWS) is a multiple congenital anomaly syndrome caused by a heterozygous mutation or deletion of the ZEB2 gene. It is characterized by a distinctive facial appearance in association with intellectual disability (ID) and variable other features including agenesis of the corpus callosum, seizures, congenital heart defects, microcephaly, short stature, hypotonia, and Hirschsprung disease. The current study investigated sleep disturbance in people with MWS. In a series of unstructured interviews focused on development and behaviors in MWS, family members frequently reported sleep disturbance, particularly early-morning waking and frequent night waking. The Sleep Disturbance Scale for Children (SDSC) was therefore administered to a sample of 35 individuals with MWS, along with the Developmental Behaviour Checklist (DBC) to measure behavioral and emotional disturbance. A high level of sleep disturbance was found in the MWS sample, with 53% scoring in the borderline range and 44% in the clinical disorder range for at least one subscale of the SDSC. Scores were highest for the Sleep-wake transition disorders subscale, with 91% of participants reaching at least the borderline disorder range. A significant positive association was found between total scores on the SDSC and the DBC Total Behaviour Problem Score. These results suggest that sleep disorders should be screened for in people with MWS, and where appropriate, referrals to sleep specialists made for management of sleep problems. © 2015 Wiley Periodicals, Inc.