Background: Obstructive sleep apnea syndrome is common in children with Down syndrome (DS). Little is known about sleep patterns, especially arousals, awakenings, and movements during sleep in children with DS. Objective: To determine the characteristics of sleep disorders in children with DS and to define the associations between respiratory disturbance and arousals, awakenings, and movements. Methods: The study included 23 children with DS, compared with 13 children with primary snoring. All underwent a 6- to 8-hour sleep study. Results: The respiratory disturbance index was significantly higher in the children with DS (28 ± 2.3 events/h vs 0.6 ± 0.4 events/h; P < .05). Sleep was significantly fragmented in children with DS, who had a significantly higher arousal/awakening (A/Aw) index (24.6 ± 7.9 events/h) compared with the comparison group (17.6 ± 4.0 events/h) (P < .02). A higher percentage of jerks associated with A/Aw and respiratory event-associated A/Aw was observed in patients with DS (45.2% ± 25% and 8.6% ± 6.4%, respectively) compared with the control patients (10.2% ± 4.5% and 1.5% ± 2.1%) (P < .02). The median length of occurrences of stage 2 sleep was 27% shorter in the DS group (P < .03). The number of shifts from 'deeper' to 'lighter' stages of non-rapid eye movement sleep was 30% greater (P < .02) in the DS group. Conclusion: Children with DS have significant sleep fragmentation, manifested by frequent awakenings and arousals, which are only partially related to obstructive sleep apnea syndrome.