Quality sleep is essential for patients with epilepsy, but this aspect of their treatment is frequently overlooked. Sleep disturbance can result in daytime drowsiness, worsening memory, and deteriorating seizure control. In a few patients, recognition and treatment of a coexisting sleep disorder can make the difference between complete seizure control and refractory epilepsy. Sleep has effects on interictal epileptiform discharges, with particular implications for diagnostic studies. Sleep disorders can coexist with epilepsy, leading to errors in diagnosis and worsening of seizures. Some specific syndromes demonstrate unique properties related to sleep. Seizures themselves disrupt sleep, even when occurring during the day, with the potential for persistent drowsiness and, perhaps, further memory dysfunction. Finally, most patients with epilepsy are treated with anticonvulsant drugs, some of which can have adverse (or beneficial) effects on sleep.