We evaluated daytime sleepiness in 26 hypersomniac patients, 100 epileptic patients, and 267 healthy subjects using the Epworth sleepiness scale (ESS). The ESS score was higher in hypersomniac patients, and no difference was found between epileptic patients and healthy subjects. The score had a weak correlation with the number and amount of anti-epileptic drugs used by epileptic patients. The patients with symptomatic epilepsy and who had a high seizure frequency reported a high daytime sleepiness. The ESS score showed a weak-positive correlation with the apnea–hypopnea index and a strong-negative correlation with the average and lowest O2 saturation during all-night non-rapid eye movement sleep in patients with obstructive sleep apnea syndrome. The ESS is a valid and convenient measure for evaluating daytime sleepiness in epileptic patients.