Typically, this type of seizure lasts between 10 and 30 seconds. The person, most often a child aged 5 to 15, abruptly stops whatever he's doing (talking, walking) and appears to "stare into space." Absence seizures rarely cause a true convulsion in which the person falls down or collapses. These "spells" may occur infrequently or several times per hour. About a quarter of people who have absence seizures will develop another type of generalized seizure called tonic-clonic seizures (formerly called ''grand mal'' seizures). The vast majority of children, however, will outgrow them.
Based on a prevalence rate of 6 per 1000, it has been estimated that there are about 96,000 people with epilepsy who require continuing hospital-based medical treatment. Of those, 15,000 will have more than one major seizure a month and 36,000 more than one seizure a month. Overall it has been estimated that there are approximately 12,000 patients with severe epilepsy and additional handicaps who may require institutional care.