Background: Sleep disturbance is common and can have harmful psychological and physical effects. While sleep problems in children with Down syndrome (DS) have received a reasonable amount of attention, very little has been written about this topic in adults with DS.; Method: The present study consisted of an online survey completed by 100 family carers of adults with DS.; Results: High rates of sleep problems of different types were reported in the adults with DS comparable to those found in children with DS in previous research. Significant associations were found between sleep problems and body mass index, excessive daytime sleepiness and a range of health and psychological problems. Low rates of treatments for sleep problems were reported. The majority of family caregivers felt their own sleep was affected.; Conclusions: Sleep problems in adults with DS are common and varied. Assessment and treatment of such problems are likely to improve quality of life.