The West syndrome was described by the physician West in his own son in 1841 and is defined as a triad of myoclonic seizures called "infantile spasms", electrographic abnormalities called "hypsarrhythmia" and arrest of psychomotor development and mental retardation. These symptoms are so pathognomonic that the impression is that the syndrome is caused by a single mechanism, but actually there is heterogeneity of etiologies, different recommendations of treatment and prognosis. The West syndrome was established as an infantiLe epileptic syndrome (ILAE Task Force, 1989). Infantile spasm is the most common epileptic syndrome during infancy and entails 50% of all epilepsies between ages one month to one year. Its incidence is 1:3200-3500 live births. Despite its absolute definition, the variability of etiologies, clinical presentation and electrographic make it difficult to set rigid, clear treatment guidelines and research methodology. This review aims to present modified hypsarrhythmia, the etiologies and prognosis of symptomatic infantile spasms, and emphasize the importance of early recognition of modified hypsarrhythmia by surveillance of electroencephalograms.