A method of treating or preventing Obstructive Sleep Apnea (OSA) comprises the administration of a pharmacologically effective amount of zonisamide to a patient in need thereof, with the proviso that OSA caused by external mechanical obstruction of the airways, such as by mucus, is excluded. Also disclosed is the use of zonisamide for the manufacture of a medicament useful in the treatment; a protective patch comprising zonisamide and a pharmaceutically acceptable carrier for transdermal or transmucosal administration to a person suffering from OSA; and the use of zonisamide for the manufacture of a diagnostic device, kit or composition for the diagnosis of sleep disordered breathing.