Background: Sleep problems are common in individuals with intellectual disability. Little is known about sleep in children and adults with Cri du Chat syndrome (CDC). Method: Sleep was investigated in 30 individuals with CDC using a sleep questionnaire. Sleep problems and sleep behaviours in individuals with CDC were compared with individuals with non-specific intellectual disabilities (NS) (n = 30) and Down's syndrome (DS) (n = 30). Results: Nine individuals with CDC (i.e. 30%) had a sleep problem, compared with seven individuals with NS (i.e. 23%) and three individuals with DS (i.e. 10%). Though there were few differences between diagnostic groups, night waking problems were most common in CDC. Individuals with CDC frequently showed behaviours related to disordered breathing and poor-quality sleep. Several behaviours related to sleep had a higher occurrence in CDC than in DS (P less than 0.05) but not in NS. Conclusions: It is concluded that individuals with CDC do not have an increased probability of sleep problems as compared with other individuals who share similar demographic characteristics. Hypotheses about causes of night waking problems in CDC are generated and suggestions for future research of sleep in individuals with CDC are given.