METHODS: Sleep disturbances were measured in a sample of 65 youth with DS aged 6-17 years using the Children's Sleep Habits Questionnaire (CSHQ) and actigraph watches assessing sleep efficiency, sleep duration and wake after sleep onset. Behavioural challenges were evaluated through externalising and internalising subscales of the Child Behavior Checklist (CBCL) and of the Scales of Independent Behavior, Revised (SIB-R).

RESULTS: The findings demonstrated that over a period of time, sleep problems are significantly associated with both externalising and internalising behaviours as measured by CSHQ and CBCL, even after accounting for the effects of IQ and SIB-R Broad Independence. No significant correlations were observed on a daily basis over seven consecutive days, as measured by actigraphy and both externalising and internalising indices of SIB-R.