The ways in which sleep can affect epilepsy, and epilepsy can influence sleep and wakefulness, are described. Different forms of sleep disturbance have been reported in patients with epilepsy, depending on the type of seizure disorder. Confusions between epilepsy and non-epileptic parasomnias can be a particular diagnostic problem but they can be avoided. Untreated sleep disturbance is likely to have harmful psychological, physical and family effects. Screening for sleep disturbance should be routine, and leading, if indicated, to precise diagnosis of the underlying sleep disorder on which choice of advice and treatment depends.