Lennox-Gastaut syndrome (LGS) is a rare epileptic encephalopathy with a peak age of onset of 3–5 years of age. Reported prevalence rates for LGS vary widely from 1–10% of all childhood epilepsies. Incidence rates are much lower. LGS is characterized by intractable, multiple, generalized seizure types and an interictal electroencephalogram showing bursts of slow spike-and-wave, paroxysmal bursts of generalized polyspikes, and a slow background. All patients have tonic seizures during sleep that may be subtle, and nearly all have treatment-resistant, lifelong epilepsy. Cognitive stagnation and behavioral problems are seen in almost all patients and lead to a life of dependency. The differential diagnosis includes other symptomatic generalized epilepsies and pseudo-Lennox syndrome. Misdiagnosis is common. Children and adults with LGS have an enormous impact on their families, and efforts to improve the quality of life for these patients are complex.