How often does LGS occur and who develops it?

  • The prevalence (the number of existing cases per year) is 0.26 per 1000.
  • One out of ten children who have epilepsy beginning in the first five years of life will be diagnosed with LGS.
  • Overall, LGS makes up 2-5% of all childhood epilepsy.  
  • Seizures usually begin at 26 to 28 months old with the vast majority starting before 7 years old. 
  • Having other developmental or intellectual problems increases the chance of being diagnosed with LGS.
  • In adults with cognitive problems who live in supported facilities and are unable to live independently), up to 17% have LGS.
  • Slightly more males have LGS than females (prevalence rate of 0.1 per 1000 for boys, 0.02 per 1000 for girls).
  • There are no racial differences. 


Seventy to eighty percent of people with LGS have an identifiable cause for the syndrome. A cause has not been found yet for the remaining 20 to 30% of people.  

  • 17 to 30% of patients have a history of infantile spasms. These children have a significantly worse prognosis.
  • LGS has many causes, many of which are associated with diffuse brain injury. Typical examples of underlying causes include encephalitis, meningitis, tuberous sclerosis complex, brain malformations, perinatal injury including hypoxic-ischemic (deprivation of blood flow and oxygen to the brain) encephalopathy, trauma and frontal lobe injuries. The cause associated with the syndrome will likely affect the prognosis, and sometimes how to treat it.
Reviewed by: Joseph I. Sirven MD / Patricia O. Shafer RN MN on 6/2014