Attempts to analyse the sleep structure of patients with eating disorders have so far led to conflicting results. Polygraphic findings suggest that patients with bulimia nervosa are not easily distinguishable from age-matched controls, whereas anorexic patients show some abnormalities in sleep efficiency and sleep architecture. Nevertheless, both bulimic and anorexic patients complain of poor quality sleep. The aim of this study was to evaluate the microstructure of sleep in anorexia and bulimia by analysing arousal (following the rules of the American Sleep Disorders Association) and the cyclic alternating pattern (CAP). The results confirmed the presence of sleep disturbances in eating disordered patients: an increase in arousal length and the CAP rate. They also seem to confirm the findings of previous studies suggesting that altered sleep in eating disordered patients may be related to their body mass index (BMI) and psychopathological status.