Infantile spasms (IS) are a distinctive form of seizure disorder, mainly observed in infants, in the first year of life, and refractory to conventional antiepileptic drugs. IS are manifested as clusters of increasing plateau-decreasing-intensity brisk flexions or extensions of the neck, with abduction or adduction of the upper limbs. IS must be differentiated from rarer, earlier-onset conditions with ominous prognosis, such as early infantile epileptic encephalopathy and early myoclonic encephalopathy. Differentiating IS from the tonic seizures of Lennox-Gastaut syndrome may be difficult, especially when the attacks are in extension and not repeated in clusters. West syndrome may evolve into Lennox-Gastaut syndrome. The prognosis of IS is heavily influenced by the pathological process underlying the syndrome. Brain MRI has a high prognostic value, which is closely linked to its diagnostic power. Randomized clinical trials in Lennox-Gastaut syndrome have been performed for lamotrigine, topiramate, felbamate, rufinamide, thyrotropin-releasing hormone (TRH) analog, and cinromide.