Previous studies on the characteristics of disturbed sleep/wake patterns in children with the Rett syndrome have yielded inconsistent findings. In the current study, momentary time sampling procedures were used to measure the sleep/wake patterns of 20 girls with classical Rett syndrome. These patients had significantly more total sleep than age peers (M = 110.1; Zm = 2.58; p = .01), significantly less nighttime sleep (M = 80.8; Zm = -7.53; p less than .0001), and significantly more daytime sleep (M = 24.5; Zm = 8.71; p less than .0001). Night sleep was negatively correlated with age (r = -.59; p less than .01); day sleep was positively correlated with age (r = .54; p = .01). These girls also displayed night wakings on 20.9% of nights, delayed sleep onset on 67.8% of nights and early wakings on 24.5% of nights. These data clearly demonstrate that children with the Rett syndrome have markedly impaired sleep/wake patterns and suggests that the sleep dysfunction may worsen over time.