Aim:The aim of this study was to retrospectively evaluate clinical features, treatment and prognosis of 20 patients followed up as Lennox-Gastaut Syndrome in ESOGU in the Division of Pediatric Neurology. Material and Method: Multiple different types of seizure, diffuse spike-wave pattern(<3 Hz) on electroencephalogram, psychomotor retardation were the diagnostic criteria for Lennox-Gastaut Syndrome. The patients who had no etiologic reason were described as the idiopathic type. Prenatal, natal and postnatal risk factors, seizure and clinical features, neurodevelopmental status, treatment and prognostic features were evaluated. Results: Thirteen patients were female, seven were male; male/female ratio was 1,9. Nineteen patients were described as the symptomatic type. Hypoxic ischemic encephalopthy was the most common risk factor. Sixty percent of the patients had a history of infantile spasms. Generalized tonic, generalized tonic clonic and atonic drop attacks were the most common seizure types. Speech impairment and microcephaly were the most frequently seen neurologic findings. Diffuse spike-wave activity (1-3 Hz/s) on EEG, bioelectrical status epilepticus and 9-14 Hz/s fast activity discharges were the most commonly seen discharges. The most common neuroimaging finding was cerebral atrophy. Sixty percent of the patients suffered from a large number of seizures per day despite multiple antiepileptic drugs. The most commonly used antiepileptic drugs were valproate sodium, clobazam, lamotrigine and topiramate. Conclusions: The prognosis of Lennox-Gestaut Syndrome is poor due to either recurrent seizures or mental deterioration. Seizure control can not be provided despite the use of multiple anti-epileptic drugs. New antiepileptic drugs are needed. (Turk Arch Ped 2012; 47: 49-54)