West syndrome or West's Syndrome is an uncommon to rare epileptic disorder in infants. West syndrome was named after the English doctor and surgeon William James West (1793-1848), who lived in Tonbridge. In 1841 he observed this type of epilepsy in his own son, James E West, who was approximately four months old at the time. He published his observations from a scientific perspective in an article in The Lancet. He named the seizures "Salaam Tics" at the time.

Other names for it are "Generalized Flexion Epilepsy", "Infantile Epileptic Encephalopathy", "Infantile Myoclonic Encephalopathy", "jackknife convulsions", "Massive Myoclonia" and "Salaam spasms".

The term "infantile spasms" can be used to describe the specific seizure manifestation in the syndrome, but is also used as a synonym for the syndrome itself. West syndrome is the triad of infantile spasms, a pathognomonic EEG pattern (called hypsarrhythmia), and mental retardation - although the international definition requires only two out of these three elements.

The syndrome is age-related, generally occurring between the third and the twelfth month, generally manifesting around the fifth month. There are various causes ("polyetiology"). The syndrome is often caused by an organic brain dysfunction whose origins may be prenatal, perinatal (caused during birth) or postnatal.

Prevalence is around 1:3200 to 1:3500 of live births. Statistically, boys are more likely to be affected than girls at a ratio of around 56:44. In 45 out of every 50 children affected, the spasms appear for the first time between the third and the twelfth month of age. In rarer cases, spasms may occur in the first two months or during the second to fourth year of age.